Yep. I'll be rebuilding out 59 this spring. Once it's rotted, especially at the ends you have to replace the wood. The way they are built the wood deck sits on the frame and the rest of the body sits on that. If the deck has rotted then the body droops and strat damaging it.
Go look in the floor repair section. williamhenchel has TONS of pictures posted. I'll be documenting the 59 rebuild as well. Just have to get some other stuff done before I can delve into this fun.
If it's just at the ends you can replace it but just replacing the last few feet but to get the best results in reguards to strength it's best to put full width of the trailer sections.
1959 22' Caravanner
1988 R20 454 Suburban.