We had a 2005 Cougar that had a similar rear wall as the one you are looking at. We had a ripple in the rear wall too. I called Keystone and they said that the rear exterior wall is not glued to the wall supports and is "free floating". Over time, the fiberglass can develop those ripples. So I would not be concerned about the rear wall so much. However you do certainly have rot in the roof as the video showing you pushing on the roofing material with no backing underneath. At the least you'll need a new roof and underlayment. You won't know the extent of the damage until you strip the roof. RV Roof in Florida can install a new lifetime roof for a few thousand dollars. When I was looking at that option, it was around $5 grand for our 28' Cougar. Depending on what you can buy the rig for it might be a consideration. But like someone else posted, there are a lot of preowned RV's for sale.