I couldn't find a good picture of a Scamp
bunk bed, but I believe (hope) it is similar in concept to the Casita
front bunk; I assume the upper bunk is held in the position with two metal poles. If my assumptions are correct, then perhaps the following will be of help.
This picture shows my idea, sorry it is pretty crude. The red lines represent white PVC pipe, I used red lines for clarity. The concept is to assemble a bed rail with rails for both the upper and lower bunks. The metal bunk support poles will be inserted into the hollow vertical legs of the bunk bed rail assembly and the beds will be left in the up position. If you can't travel with the bunk beds in the up position then selected joints of the bed rail assembly can be left unglued so that it can disassembled for storage. I assume the beds will be left up so I didn't account for disassembly in my notes below.
I would take the bunk bed support pole to the hardware store and see which size of white PVC pipe fits best around the outside of the bunk bed support rail, I hope a 1 inch PVC pipe works. There are two different types of PVC pipe, Schedule 20 and Schedule 40, they both have the same outer diameters but have different inner diameters as the Schedule 40 is thicker, I suggest you use the Schedule 40 if possible. The bunk bed support pole doesn't have to fit tightly into the PVC, a little slop may be better as it will make installation easier. The hardware store folks can help select the pipe and other items. You could use copper pipe, but PVC is easier to work with.
If the bunk bed support pole does fit into a PVC pipe, then I suggest buying the following:
8 Slip Fit T Fittings (No threaded sections)
4 Slip Fit Elbow Fittings (No threaded sections)
4 Slip Fit Female-Female Couplings (No threaded sections). These will come in handy for splicing pipe sections together to correct errors or optimize the use of available pipe material.
PVC Pipe Cutter
PVC Pipe Cement
I like two rails for each bed for both safety and structural reasons. I assume you will need to buy two 10 foot sections of PVC pipe. You can easily determine your requirements by measuring the distance between the posts and multiply by 4, then measure the distance from the bottom of the lower bunk to 8 inches above the upper bunk and multiply by 2. The total should be pretty close to what you need.
When assembling the rails, the only critical dimension is the distance between the posts, for everything else as long as the left side matches the right side you should be OK.
The long vertical legs of the rail will be hallow so can insert the bunk bed support poles through the rail before you put up the bunk bed. The bed rails should be high enough to keep kids from rolling over it but not so high that pressure on the top rail can provide enough torque to cause failure. I suggest the space between the bottom rail and the mattress, and the distance between the rails be no more that 2 ˝ inches.
After you cut all of the PVC pipe (easy to do), I suggest you assemble to pieces together and install it in the trailer. You can then disassemble the upper rail and glue it back together piece by piece. DO NOT GLUE ON THE LOWER ELBOW FITTING. The elbow fitting will be glued on last to allow for final adjustments to the rail assembly. You don't need to use much glue, in fact you should use as little as possible. Be very careful to not spill any in the trailer. If the pipe section fit tightly together you may not need to use any glue, but I would just for the added security.
After the upper rail is assembled, remove all pieces and assemble the bottom part of the rail. DO NOT GLUE ON THE UPPER ELBOW FITTING, this is the same elbow fitting discussed above.
Reinstall the partially completed rail assembly and tweak the unglued elbow fittings as required to get the upper and lower rails to match. Glue the elbow fittings in place and you are good to go.
I think this will work, let me know if it works out. Post a picture if you can.