Just sold a palomino camper with soft floors. Had what they called bonded floors which is Styrofoam with thin ply wood attached. Can't repair them because seams won't hold as that floor gives a bit u...
I think most ultra-lights use that type of construction. My 2003 Gulfstream Streamlight had the bonded floors. The floors felt spongy from day one. I traded the camper after one trip.
My first and last ultra-light. Most regular trailers use plywood/MDF over wood floor joists.