bunk beds in a Sovereign?

[1moreRon]

My wife and I bought a 1974, 31' Sovereign and have adopted a couple of children since the Airstream purchase. I want to put a removable bunk bed, secured to the walls, above the couch/bed but am having a difficult time trying to locate a solid structure inside the walls to anchor the bed frame (the plan calls for mounting a metal strip on the wall and then connecting a homemade bed frame to that so that we can put it in and out in less than 1 minute).
I was told that there are studs in the wall, the separate the outside skin from the inside skin, that I can anchor the bed supports to but after tapping the wall I can't find anywhere I'd trust to be a wall stud - even a 1" x 2".
Or has anyone else found a better way to put bunk beds inside one of these?
Thanks