I took the opposite tactic than most mention here (junk it). I looked for a trailer with damage so I could restore it and configure it the way I wanted. The restoration effort, with pictures of framing and floor rehab are in the "Cowboy/Hilton" link in my signature line.
The chances that you don't have water damage inside the walls are slim-to-none. Remove the wall paneling (you will need to do this anyway to rehab the floor) and inspect for leaks from above. If you have a metal belly panel, they can be repaired by installation of new aluminum sheet attached with fasteners into the new floor joists you'll be adding.
The usual nature of TT construction is that the walls are fastened onto the floor sheathing. This necessitates a bit of screw/nail/staple removal. A reciprocating saw and a small grinder will be your new best friends. The new subfloor can be reinstalled (slid) under existing wall framing and the walls reattached.
The project is totally doable and anyone that can build a doghouse can restore a TT. Heck, a good Farmer can fix anything! Good luck with your project, you can message me or post here if you need any help.