Rotting floor in our 2008 Jayflight 26BH

I feel your pain on the leak. We had a 2010 Jayco FBS that leaked in the same area yours was leaking. I had to remove and replace the paneling which I was fortunate enough to find a match at a dealership in Kansas City, rebuilt the wall studs because of rot and replaced a 2'x4' chunk of flooring which all told took about 4-5 days. And FYI the tool I used was an Oscillating Multi Tool to cut away practically everything and it worked great in tight spots and cutting away the rotted floor, floor wall plates and studs. Also pulled all the windows over a period of time and resealed them with Butyl tape which to me made a tighter seal than the foam tape used in the factory. I also found out the leak was a caused by a small hole in the caulking on the bottom of the front cargo access door. The water ran off the top of the cargo door down it's side then entered in the hole and followed the floor wall plates causing a lot of damage over time. My opinion was that the leak was caused by poor factory caulk installation and started on day one on the assembly line. Also if you are interested you can view pics of the repairs I did on the Jayco Owners website under Agggghhh, discovered a water leak