in 2011 I built a Tear drop trailer (TD) similar to this https://www.instructables.com/id/Teardrop-Travel-Trailer/ , most TD campers carry some sort of air conditioner to deal with the hot weather. In dry areas of the country a swamp cooler works fine as blowing a fan over a block of ice will cool the air and any moisture picked up from the ice will feel nice.
In humid areas of the country a swamp cooler just adds to the misery, I remember spending a few weeks in Mena, AR at a paint shop. At 97 F and 90% humidity the sanding crew was dying from the heat in the shade, so the boss went out and borrowed or rented a swamp cooler. As I was just observing our aircraft being painted I could sit right in front of the swamp cooler all day, from walking around I discovered that the cooler feeling air only lasted about 4-6 feet from the cooler, after that the breeze felt ok and more than 10 feet away all you got was the noise of the huge fan.
The swamp cooler was about 6 feet square, it had a 5 foot tall fan blowing through some sort of paper strips that were being saturated with water being pumped over them from a large tank in the base. the base tank needed to be hooked to a garden hose to keep it from going dry. For all the water being evaporated I think the swamp cooler just made it worse inside the paint shop, and it made the paint jobs have problems.
the main reason air conditioning feels so nice in humid areas is that the air conditioner removes quite a bit of water vapor, dry air allows you to sweat, which is the way your skin gets rid of extra heat. Just look underneath your car or air conditioner and you will see a puddle on a hot humid day. In fact modern cars run the air conditioner on low when you select "defrost" to remove the excess moisture.
For those of us who don't want to lug an air conditioner in our trailers (or tents), and where a swamp cooler won't work, or where you would need a 50 mile extension cord or deal with a generator, I took a few different ideas from Instructables.com and put them together in my car.
Being from Maine, I bought a new car without air conditioning, since we only need AC for a week or two up here almost 25% of cars are sold without AC, saving about $800. Since then I got a job in central NH where the weather is much hotter than coastal Maine. I decided I needed some AC.
I bought a used heater core off of fleabay for $25, a cooler that would fit between my kids booster seats in the back seat $35, two computer cooling fans for $15 fleabay, and a 12 volt live bait well pump $30 wallyworld boating isle. When assembled as shown the heater core blew cold air on the back of my head, but was not enough to cool off my car with it's untinted windows and blazing sun shinning in. I also thought my heater core was garbage as water streamed from it while it was running, after pressure checking it I found it was still good, I had been condensing tons of water out of the humid air.
While this was a failure, I learned a few things, that if applied to a well insulated area (inside my TD which if you made it a cube would only be 160 cubic feet (5' W X 8' L X 4' H)) will work as long as enough ice is used.
I modified my "air conditioner" into a "body cooler" and now it works great, and the ice lasts forever.

Step 1: What Are You Hacking Together?

to build a 12 volt air conditioner or body cooler you will need mostly the same items..
-flexible hose and clamps
-12 volt bait well pump (I bought the 500 gph model, way over kill on the flow rate but cheap)
-wiring
-cigar lighter plug
-largest cooler you can fit in the area it will sit. (air conditioners are rated in BTU's, the smallest ones for sale cheap are the 5,000 BTU ones, house and larger ones are rated in tons, this air conditioner will depend on how much ice you can put in it) I found the "marine" coolers the best for what I needed as they tend to be all white (less solar heat gain) and much more rectangular with less bulk (takes up space) mine also has large easy to hold handles (easy to strap into the seat belt in the car, and easy to carry full of ice and water) it also has an external hinge, most hinged lid designs have a air leak around the hinge, the external hinge type have a lid that will lock in place even if you remove the hinges.
-zip ties

for a 12 volt air conditioner you will also need:
-a car heater core (mine was from a jeep Cherokee, I figured one from an SUV or van would have a larger heat exchanging area than one for a small car)
-as many 12 volt fans as it will take to cover the grid section of the heater core.
-12 volt switches or a house thermostat (if you want the fan to go on and off at a certain temp)
-a drip pan that is larger than the heater core and some sort of drain line to carry condensation back to the cooler

for a body cooler:
-small diameter PEX plumbing and fittings (I used 3/8" but now I see 1/4" in some hardware stores)

Tools:
drill and hole drills
screw drivers
wire crimpers
pex ring crimpers (if you use pex) (my crimper is a two part C shaped set of jaws that you squeeze using vice grips, it has spots in it to crimp 3/8", 1/2", 3/4", and 1" pex copper crimp rings.

Step 2: Making Your Heatsink

just like dark is the absence of light, cold is the absence of heat.
- Remove the hinges from the cooler lid, mine came off with screws so it was easy. You want the pump, wiring, and return tube, all connected to the lid so it can be left in place while you go fill the cooler with ice and water.
-Put the 12 volt pump in one corner of the cooler, if the cooler will be sitting on a seat or other tilted area put the pump at the lowest end.
-connect the flexible tubing to the outlet nipple of the pump and secure it as needed (the pump I have has the nipple coming out the side, I used clear plastic tubing to connect on to the nipple, and then a plastic pex 90 degree elbow to run my tubing vertically up to the cooler lid.
-mark the lid of the cooler where you want to run your tubing through it.
-drill the smallest hole you can get the tubing through to minimize air leaks.
-drill another hole in the lid, right next to the first one, or at the opposite end, it is more convenient for me to have both hoses next to each other, however to make sure the water is going through all of the ice I added a 90 degree elbow to the hose to shoot the water at the opposite end of the cooler from the pump.
-seal the holes in the cooler lid with RTV

Step 3: Cooling Off a Tear Drop Trailer

-install the heater core where you want it, I plan on having mine installed near the top of the galley wall in the galley, with a vent into the TD sleeping compartment.
-mount your 12 volt fans so they blow through the heater core. I plan on one fan bringing in outside air all the time, and the other recirculating air from inside the TD.
-mount a drip pan underneath the heater core with a drain line back to the cooler.
-run the wires from your 12 volt power source to a switch or two. I plan on having my TD have two fans both running continuously, one bringing in fresh air the other recirculating TD bedroom air, and a wall thermostat switching the 12 volt pump on and off. This may exceed the amps rating for a normal wall thermostat but they also sell 120/220 V wall thermostats that will work.
-run the plumbing from the heater core to the cooler and clamp the ends if needed.
-zip tie everything in place as needed.
-fill the cooler with ice or ice packs, I use juice bottles full of water (fill 3/4 full, dump in salt and shake until the water won't absorb any more, put the lid on and freeze with the bottle on its side) leave a space for the pump (I plan on making some sort of baffle to keep ice away from the pump )
-put in enough water to cover the top of the pump.
-put the the cooler back together, turn it on, check for leaks.
-enjoy hours of cool air in your TD.
since a TD is mostly used inside for sleeping, a cooler full of ice should last the night, however you will probably have to refill the ice and dump out most of the water from the night before. Since most campgrounds, and gas stations have ice for sale this shouldn't be too hard.
I have posted this idea on tnttt.com and one guy has tried it, http://www.tnttt.com/viewtopic.php?f=29&t=18104&hilit=rowerwet&start=15 the guy who tried it is near the bottom of page 2 of the thread
his quote " I used 10lbs of ice and it lasted about 5 hours at 88 degree's outside, my Tear maintained 76 degrees." He goes on to give ideas on how he wants to improve the design using a copper coil inside the cooler instead of a large bath of water, to do that though would require some sort of reservoir for expansion of the water, not hard, just a little more details, is all.
just like my other I'ble on how to heat a TD or tent off the grid, this gives a way to cool a TD off the grid. In fact ice was around a long time before refrigerators, my parents house is built in the area that an ice house once stood hundreds of years ago. During the New England winter ice was cut out of the pond behind their house and packed in straw and saw dust in double walled ice barns, the ice was even shipped all around the world in old sailing ships packed in straw and sawdust to be sold.

Step 4: The Body Cooler

this is my current design instead of air conditioning in my car, it is a direct copy of this I'ble https://www.instructables.com/id/Too-Hot-Remove-heat-from-your-body-with-the-Back-/ only mine uses pex as the heat exchanger, this works very well, almost too well, I have had to unplug it more than once while driving on very hot days, as I found I wasn't sweating anymore and was starting to feel a little sick to the stomach. a timer circuit or some sort of clip on body thermostat might be a good idea.
IF YOU HAVE CIRCULATION PROBLEMS THIS IS NOT A GOOD IDEA FOR YOU! IT WORKS TOO WELL AND COULD KILL OR BADLY HURT YOU.
After my heater core Air conditioner idea failed due to the heat coming in through the window glass, I took the heater core off of the cooler and made a back heat exchanger this way:
-measure the length of the nipples on the T fittings with the tips touching,
-cut a short piece of PEX to cover that length and install it on the nipples with a PEX lock ring.
-crimp the ring in place with the pex crimper.
-continue the string of T fittings with all of the T lower legs pointing up until you reach the width of the seat back it will be installed on.
-for the last pipe you need a 90 degree fitting instead of a T fitting.
-count the number of T's and put another string together that matches the first string you made
-measure the height of the seat back and cut the small diameter PEX tubing to length
-install the PEX tubing to the T legs to connect the upper and lower runs, with the exit for the water at the top opposite the in for the water at the bottom.
-I used two 90 degree PEX fittings at the top to turn the water return 180 degrees behind the headrest of the car seat to lock it in place.
-connect the lower and upper supply/return lines to the flexible tubing coming from the cooler
-run the wires from the cigar lighter plug to the pump. an inline switch might be nice as it would save plugging and unplugging the cigar lighter every time. my cigar lighter plug has an LED in it to let me know it is getting power. The first time I used it I bumped the cord and the fuse inside the plug blew, since I knew my cell phone charger still worked that meant the plug had the open, which turned out to be the fuse.
-fill the cooler with ice and just enough water to cover the pump
-put the pump in the cooler so it is at the back in most cars, as the seat slopes toward the back.
-this design is so efficient that you could easily us a very small cooler, or do all of the seats in the car, and since the pump is rated for 500 gph it would handle all four, just install a simple in line ball valve for each seat back to regulate flow if no one is sitting there.
this set up works great and you really don't notice the pipes as the seat back lets them sink in.
-I like having clear plastic supply lines also as they let me see that water is flowing, however they are not rigid enough to keep from being collapsed by my weight against the seat back, PEX is very rigid, I could probably stand on a PEX pipe, and even if it did collapse it would just snap back.
running the water from the bottom of the seat back to the top ensures that it is always full, if it ran from the top down the water could drain through the first few tubes and leave the last few empty.