Introduction: Mobile Cabin - a Simple RV Trailer
Here is a straight-forward solution to a problem I faced. As i get older, I needed a comfortable place to sleep when I head into the woods. I no long look forward to sleeping on the ground in a tent and needed something to fill this basic need. Where I go to make maple syrup for instance is completely undeveloped (and can get very cold!). No electricity or running water is available so my portable shelter has to be self sufficient.
My solution to this challenge was to build a small trailer that is light enough and small enough to be easily trailered behind my small SUV. It also needed to be low cost and reasonably easy to assemble. I already owned a 5 X 8 foot Northern Tool trailer, so this was the starting point of my solution. Keeping the trailer the same cross section of the vehicle makes the drag not very important and means the trailer will follow easily behind me as we meander down those back country dirt roads. Others have made similar RV trailers, but have either made them using house construction techniques, complicated tear drop designs, or using expensive materials. My design cost approximately $700 and took me 5 weeks of working a few evenings per week to complete.
Step 1: Building the Removable Deck.
The first step was gather all the materials. A complete list is in the Appendix. My existing trailer already has a 5/8 plywood deck that is then the starting point for our design. The RV trailer is bolted to this platform thus making it removable so that the trailer can still be used as a stand alone trailer again.
I used pressure treated 2" X 2" X 8' to form a grid on top of 5/8" pressure treated plywood. Exterior grade deck screws and Liquid Nails glue were utilized. It should be immediately obvious that a 4 foot wide trailer would be more material efficient than my 5 foot trailer since I needed two sheets of plywood for the 5 foot wide deck. However i suggest the 5 foot approach because the bed will take up 80% of your space and i want to be able to fit a few other essentials in my trailer. The spaces between the 2"X2" were then filled with one inch insulating foam board. The board is both glued and screwed into the plywood. After drying, the whole assembly is flipped upside down and bolted to the existing trailer deck and is the basis of my removable design..
Step 2: Building the Walls
Each of the four walls was built individually on top of the trailer. The walls are constructed ot 1/4 " B/C X (exterior grade) plywood. Exactly 1 inch tall by 1.5 inch wide lumber was ripped from 2"X4"X8' fir/spruce lumber. A one inch lip was left on the plywood bottom so that it would overhang the deck and allow for secure fastening to the deck. Windows and doors were also framed in at this time. 1 inch exterior deck screws were used to hold the plywood to the frame along with construction adhesive..Every piece of wood and foam in this build was glued into place. Wood was also always screwed together. This sandwich construction build up of materials make for a very light but ultimately very strong structure. Note that a pilot hole and counter-sinking were necessary to avoid splintering the thin plywood. One inch foam board was glued into all empty spaces. Assembling these wall panels while laying flat allows for the simple method of allowing gravity to hold the insulation in place while the glue dries.
Step 3: Assemble the Walls
The four walls were then stood up one at a time. They are screwed in to the deck and through each corner using exterior grade deck screws. The openings for the doors and windows were then routed out. 2"X4" are then installed as the ceiling joists. Note that only a couple are necessary at this stage to do the routing of the openings while all of them are necessary before the ceiling and roof can be installed. A frame for a vent was put in to enable that addition later.
Step 4: Ceiling and Roofing Install
1/4" BCX plywood was then cut and installed to form the ceiling. This step takes two people, one to hold the plywood up from inside the trailer and the other to screw it in place. The opening for the ceiling vent is then cut out. Insulation is then glued into the open spaces. I also used foam sealant to make sure all gaps were closed in the insulation space. The wiring from the battery to the two LED light fixtures was then installed in the roof cavity before finishing the roof with more 1/4" plywood. The opening on the roof for the vent was then routed out. EPDM roofing material ws then laid out on the roof. It is easiest to fold it back on itself halfway to spray on the contact adhesive. You then slowly onroll it and press into place. The second half is then rolled up and the gluing step repeated. Trimming the edges and removing the EPDM form the vent cutout is next. The rubber like material is fairly easy to cut with a standard utility knife. The vent is then screwed through the EPDM materal to produce a watertight seal. If only EPDM was used as the roofing material, you would put it on top of the vent and wrap it over the edges of the roof. But because we are using aluminum flashing on top of our roof,. we trim to exactly the edge and put the vent on top of the EPDM.
Step 5: Windows and Doors
Doors were then cut out from 3/4" BCX plywood. Two batten were then attached to the inside of each door to provide stiffeners since flatness is necessary for a good door seal. Square molding 1/2" by 3/4" was then added to each door opening to provide a door jamb. The first of many coats of exterior stain/sealant was then applied to the exterior walls and the door panels.A good quality silicone sealant was applied to the lip around each window. The windows were then screwed into place and clamped in place till dry. The doors were then attached using exterior grade hinges, bolt lock and pull. A tip here is to use small pieces of cardboard to shim the door in place while installing to get the desire clearances. A second coat of stain was then applied. A simple hook and eye were installed on the interior of the doors to hold them closed from the inside. Make sure to lock your bolt in the open position when you are inside so your “friends” can’t bolt you in. Lol
Step 6: Interior Features
A battery restraining area was then formed by 1" X 1.5" wood and screwed into place in one of the rear corners. A similar restraining board set was screwed into place for the bed. LED lighting was then installed near each door opening. A small wall and the surrounding area was then lined with cement board. This is to mitigate the fire risk in such a small area. Even though the heater will only run for short periods of time and will be under constant supervision, safety first! In this same context, both CO2 and burnable gas sensors will also be installed. I had some old automotive carpet left over from a previous project I just tacked into place.
Step 7: Interior Walls
Insulation was added to the inside of both doors. More of our often used 1/4 BCX plywood was used to sheath the remaining interior walls and the interior doors. The CO2 and gas detectors were then mounted on the rear wall away form the heater as recommended by the manufacturer of the detectors.
Step 8: Aluminum Sheathing
Each of the four exterior vertical corners was then sheathed with aluminum. I purchased a roll of 24" wide by 50 ft long white aluminum roll. Other colors are available but are usually more expensive and special order. A large brake would be ideal for this job if you have one or access to one. I did not and so a small hand held seaming tool was used to make our bends. Cutting and bending the aluminum is an easy job if you have the equipment. A reasonable job can be done by hand but will simply take longer and not look as professional. A “Z” seal is formed for each piece of aluminum to interlock with the adjoining piece that form the roof. A large bead of flexible adhesive sealant and roofing nails attach all sheathing on the exterior edges. Note that a small lip was formed on the aluminum where it overhangs the doors and windows. This acts as a drip edge for the roof in those areas.
I chose to paint the vertical aluminum the same color as the rest of the trailer. You could leave them white for a different look. A couple more coats of paint on the exterior and we are ready for the road. Silicone caulk in the interior corners with primer and white top coat finish the interior.
Step 9: Appendix - Materials
Included here are a couple of pictures in the woods. Nice and dry after a severe rain storm blew through. This location is 150 miles from my house. It traveled well,getting 17 mpg on a vehicle that normally gets 21. (winter tires really hurt your mileage. lol)
1. 1/4” BCX plywood - 9 sheets
2. 3/4” BCX plywood - 1 sheet
3. 5/8” pressure treated exterior plywood- 2 sheets
4. 2”X2”X8’ pressure treated - 7 pieces
5. 2”X4”X8’ pine 12 pieces
6. 1”X4’X8’ insulation foam board- 8 pieces
7. Adhesive, extreme heavy duty - 3 tubes
8. Silicone adhesive - 3 tubes
9. Silicone caulk - 2 tubes.
10. Exterior grade screws. One box of 1”, 1 1/4”, 2”
11. 1/4”X3’X5’ cement board - 2 pieces
12. Exterior primer/paint combination - 1 gallon
13. Hook and eye - 2 pieces
14. Bolts with fender washers and nuts - 3/8”X6” - 4 pieces
15. 1/2”X 3/4” molding - 26 linear feet
16. 3” hinges - 6 pieces.
17. Brad nails 1” - small box
18. Door pull - 2 pieces
19. Door locks - 2 pieces.
20. 24”X50’ Aluminum roll
21. EPDM roofing material 5’6”X8’6”
22. RV windows - 2 pieces
23. 3/4 “ roofing nails -one small box
24. Led lights.
25. 12V battery
26. Mr. Buddy propane heater
27. CO detector
28. Manual ceiling vent