I don't know if we are just abnormally heavy, or our fifth wheel trailer is built strange, or we're not setting it up correctly, but every step my wife and I took inside would rock the entire camper. This was more than annoying so we looked into stabilizing jacks. There were a lot of options, but they all had mediocre reviews and cost way more than we were willing to spend. So I decided to build my own for under $25. They might not be as fancy or sturdy as the professional ones, but they definitely work.

The basic premise of my design is a set of rods that fit inside each other. After the power jacks are lowered, the clamp on the end of the larger rod is tightened. This grabs onto the smaller rod which is attached to the base of the jack legs. This additional support greatly reduces the amount of sway produced when someone moves inside of the camper. When we are ready to move, the clamps are loosened, and the jacks can raise back up without needing to remove the rods because of the way they are attached with pivot points. For my design to work, you need power jacks similar to the ones shown that have holes along the sides.

Step 1: Material Acquisition

There aren't a lot of things needed for this to work, but here is what I used.

Tools
Safety Goggles - Gotta protect those pupils!
Metal Cutter - Hacksaw, Sawzall, etc
Pliers for gripping things
Hammer
Drill with various drill bits and driver heads
Screwdriver - head required depends on hardware acquired
RV Goop (or other similar bonding substance) (Amazon)
RV Grip Tape - The sandpaper like material that is commonly found on running boards (Amazon)

Rod Materials - All Available at any Hardware Store
10' of Larger Diameter Conduit - The wider it is, the sturdier it will be...
10' of Smaller Diameter Conduit - Needs to fit easily in the larger diameter conduit
Various conduit fittings to allow larger conduit to grab on to smaller conduit - See Step 3
6 x Small "L" Brackets - See Step 4
Various Bolts, and Washers - Size depends on your RV power jacks
8 x Lock Nuts - Size depends on the bolts size
Self Tapping Screws - Must fit through holes in "L" Brackets

Step 2: Preparing the Rods

We first need to decide how long the rods will be. Yes, I said you need 10 feet of large and small diameter conduit pieces, but that means each rod will be a bit less than 5 feet [ 2 * (10 / 4) ]. You can get more or less conduit depending how long you want the rods to be. Also, the diameter of the rods will determine the stability. The wider the rods are, the less likely they are to bend, but they also cost a lot more.

WEAR SAFETY GLASSES!!!! Cutting metal pipes will cause shards of metal to fly into your face.

Cut each length of conduit into 4 equally sized pieces. That should give you 4 larger diameter pieces 2.5' in length and 4 smaller diameter pieces 2.5' in length.

Next, take a hammer and flatten one end of each conduit piece as shown in the picture.

Finally, drill a hole through the flattened end. The size of the hole should be just wide enough to allow your bolts to pass through. The size of the bolt is determined by the size of the holes in the "L" brackets (Step 4) and the holes along the power jacks.

Step 3: Adding the Grippers

The larger diameter rod needs a way to grab onto the smaller diameter rod. This can be accomplished by a series of conduit pipe fittings. I played around with various pieces until I found something worked. See the above images for the pieces I used.

The first piece slides over the end of the larger diameter rod and has a threaded end. The second piece is a coupler to connect the first and third threaded pieces. The third piece has one threaded end while the other can be tightened down around the smaller diameter rod.

I used RV Goop to glue each of the pieces together. It may be beneficial to not attach the gripper to the larger diameter rod until after you complete Step 4 - Attaching the Top 4 L-Brackets. This way, you can hold the rod up to the bracket and determine the best orientation of the gripper pieces on the rod to allow easy access to the tightening screws at the end of piece 3.

Step 4: Attach the Top 4 L-Brackets

The larger diameter rods are attached to the underside of the camper using L-brackets. These need to be screwed into the underside of the camper frame. The placement of these brackets is determined by the length of the rods. When the power jacks are full raised, the smaller rod could be completely inside of the larger rod, meaning the total rod length could be as small as 2.75' (each rod is 2.5', plus the flattened ends and the coupler section). When the jacks are fully extended, the total rod length could be up to 5'.

WEAR SAFETY GLASSES!!!! Drilling into the underside of the metal RV frame will cause shards of metal to rain down into your face.

I placed an L-bracket 4' back from each of the jacks on either side of the camper, and 43" away from the jack in the front of the camper. If you are commonly lower your front jacks quite a ways down, you may need to place the L brackets a bit closer to the jacks than I did. Also notice in the image how the L bracket is facing away from the camper. Because the two front jacks will cross each other, I suggest reversing the direction of the front L-brackets so the two front rods have clearance from each other.

Step 5: Attach the Smaller Diameter Rods

The 4 smaller diameter rods will be attached to the front power jacks. This is why the jacks need to have holes down the sides. Ours have manually lowering feet so the jacks don't have to be lowered so far, and the holes are there for the catch pin. Because our holes run through the jack legs from side to side, the two side rods can be blot directly to the legs; however, the two front rods will need to be attached to the other two L-brackets which can be bolted directly to the legs.

The L-brackets need to be bolted tightly to the legs, but the rods need to be able to pivot as the jack legs are raised and lowered. This is where the lock nuts come in handy. They don't need to be tightened all the way, just enough that the rods don't have much play room but are still allowed to pivot.

Step 6: Add the Grip Tape

Cut long pieces of the RV grip tape - a bit shorter than the length of your smaller diameter rods. Then wrap the tape around the rods like a hot dog. The tape should come with a peel off backing, so you will have to remove that part first. The grip tape helps the larger diameter rods hang onto the smaller diameter rods when they are tightened in place.

Realistically, this step could be done sooner, but I added the tape as an after thought so the pictures wouldn't have made sense.

Step 7: Attach the Larger Diameter Rods

Finally, the larger diameter rods can be placed over the the smaller diameter rods and then connected to the top L-brackets. The lock nut should be tightened as much as possible while still allowing the rod to pivot as the power jacks are raised and lowered.

To secure the rods, first raise the power jacks just slightly and tighten the third piece of the rod gripper section created in Step 3 onto the smaller diameter rod. Remember what I said at the end of Step 3 about the gripper section orientation? If you didn't listen to me, the screws to tighten the the larger rod onto the smaller diameter rod may be in a very awkward position to use...

Lastly, lower the power jacks just slightly to put pressure onto the stabilizer rods and enjoy your less wobbly camper! To loosen the rods, just loosen the gripper piece as raise the jacks like normal. The bolts connecting to the rods to the camper should be checked every once in a while, but should need to be adjusted for operation.

Be sure to loosen the rods before trying to completely raise or lower the power jacks or you could really damage something!

----- UPDATE -----
My wife and I have been living in our camper for 2.5 years now while we travel for work, and these rods are still working great. After a while, they started squeaking when the camper wanted to sway, but was stopped by the rods. This was a definitely metal-on-metal rubbing sound, and I traced the it back to the bolts connecting the rods to the L brackets. I sprayed this area with lithium grease and haven't heard a squeak from it since.