My TT (not my 5er), which I basically only use for deer hunting once a year, has sponginess from water damage in a several of places on the roof. In front from the seam (transition metal to roof material) back about 18-20 inches from one side to the other you definitely don't want to walk at all as it feels there is not much left underneath. Also 1-2 yrs ago I had to replace the outer skylight over the bath because it was cracked and was leaking causing some damage in that area. Additionally from about 2-3 inches along the edge on the driver side there is sponginess.
As I don't use it that much, I cleaned the roof with my power washer and didn't find any tears/rips or major damage other then cracking in the sealant. I elected not to replace the roof but try hopefully stop any further damage. I did an extensive eternabond application on all seams on top and along the sides followed up with Dicor lap sealant. Here is a link to the Eternabond kit I bought from Amazon - https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
The one place I wasn't able to reseal was around the A/C. Was thinking about needing to replace the seal as I felt that it probably was leaking somewhere around it. So I started to look at documentation on what size of seal I needed and how to pull the unit to be able to replace it. As I was looking at the documents, I read about that the 4 screws holding the A/C should be retightened (snugged up) every year. I found that they all needed snugging up especially one that was that was definitely looser than the other three. It was something that I had not done in the roughly 9 years I have had the TT.
I guess my point is to look at how tight the bolts on your A/C are. Don't know that is the reason for the extensive damage you have but it could have contributed to your problem.
Good luck and hope it goes well for you.
2018 Cedar Creek 36CK2 (40.5ft)
TST Cap System (Tire Monitoring)
2021 Chevy 3500HD Crew Cab 4X4 DRW Duramax (replaced 2015 Chevy 2500HD Crew Cab 4X4 Duramax)
Curt A25 5th Wheel Hitch (replaced Demco 18K Auto-slide)