My heart breaks for you with this story, I have been down the dry rot road with numerous RV projects. After buying and repairing several older RV's we bought a brand new unit that leaked from day one unbeknown to us and it took 5 years before it became unusable. Luckily the manufacturer rebuilt our RV at no cost to us, but we know most manufacturers would not do this.
The sad part is, most leaks go undetected for a long time, and even if you find the obvious cause of the leak, there is a lot of moisture still in the structure after you seal it up. I recently attempted to rebuild an RV as a project, I have a large shop I can work on RV's inside. I parked the RV inside, turned on electric heat inside and waited 6 months to start work. When I removed the outside skin, the foam and fiberglass insulation was still so wet I could ring it out.
The damage was so extensive, the more I opened it up the more I realized that my little repair job was going to be much more than I wanted to do. I had to factor in my time and materials and it made sense at that point to just scrap the RV, though I did love it. I actually made more money selling components on Craig's List than what I paid for it originally, but here again a person has to have time and space and know how to sell things with quality pictures.
Sadly, you are in a tough spot. If you are only into the trailer for a couple thousand, enjoy it while it's still usable, don't put too much into it. Yes there may be mold in the walls, but make sure you sleep with windows open and keep it ventilated.
Is it a stick and tin trailer, or a smooth sided fiberglass exterior? Stick and tin trailers are easy to repair, vacuum bonded fiberglass exterior units are much harder to work on because of delamanation issues after leaks.
All the best, Hans
