Since a picture is worth...
Here's mine during the build stage, using the Euro Military surplus cots from Coleman's Military Surplus.

The treated, heavy burlap is sewn, overlapping heavy gauge wires down both sides, and ends. The wires are hung on multiple hooks that rest in holes in the top of the heavy gauge pipe.
Finished product: Outer edge hung from e-track mounted in ceiling, spread across 4 joists. I had designed them to "clip" out of the wall e-track when not needed. Unplanned benefit: I can unclip the hanger from the e-track in the ceiling, re-clip it into the wall, above the bunk, then simply pull my hanger strap tight, and the cots rotate up against the wall to create loading room in the trailer. I've never had to take the top bunks out to use the trailer for moving stuff.

Homemade support for the vertical e-track:

These were originally designed for our kids, we "adults" slept on a click-clack Serta sofa in the front of the trailer. Now that the kids are grown/gone, we discovered the amazing comfort of the military cots. They had it made, all this time, and we never knew it!
