Unfortunately your going to have to pull up the floor and get rid of the insulation under there. I'm in the process of rebuilding (remodeling) my 5th wheel. First on the list was the bedroom leak which wasn't evident until I removed the panelling. I ended up rebuilding the entire left front corner and reinsulated with rigid insulation because it will not hold the moisture like fiberglass will. I also found that the fresh water tank had been leaking for years before I got it and it had dryrotted the entire back right corner of the trailer. All the wall supports were completely gone and I had to jack up the side wall of the trailer to original specs (it was sagging just enough not to be noticable) so that I could rebuild the bottom wall plate. I worked from the outside on this issue and the inside on the bedroom issue. But the good thing is that I'm learning alot and able to customize the layout to my own specifications and it's kind of fun. I'm nowhere near being done with it (still have to pull out the old linoleum and carpet throughout the trailer) but the way I look at it's a learning experience and I'll know what to look for in my next trailer to avoid the pitfalls of buying a used trailer.
Don't be discouraged by my situation, as one member here told me, "everything is fixable" and the parts to fix your trailer are not that expensive. If your even a little bit handy with tools, you've got no problems. This site will be very helpful, it has been for me. If you need any help, please do not hesitate to contact me.