If you want to just move the fiberglass
shell and it is flimsy, you may have to install some temporary bracing inside of the shell. Build a frame from some 2x4 or 2x2 fairly tight to the outside edges of the floor and the roof, then cross brace with more wood in an X pattern from side to side a couple of feet from each end and from the center to the ends. A bit of extra work, but it should be enough bracing to carefully lift it from the frame, maybe slip some 4x4 posts under and move to a flat area to reframe the interior. If you use screws for the bracing, the wood you use for bracing can be reused for your framing.
Unfortunately it is the interior cabinets that give trailers their structural strength. Even stripped the fiberglass
shell probably still weighs 300-400 llbs.
If you have friends like mine, when you are ready to move the shell, call them up and offer them pizza and beer for about 10 minutes work. You should have no trouble getting enough help to lift and move the shell!