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...
My FunFinder (Cruiser RV ) trailer has 5/8" tongue-groove marine grade plywood as the floor. It is undercoated on the bottom surface before it is bolted down to the frame.
This trailer is marketed as a lightweight design, for whatever that is worth.