I removed all flooring and framing with any damage and replaced. Some edge material was hard to get to. I used MinwaX WOOD HARDENER to liberally coat those areas. it's thin and soaks in, turns the wood to plastic. Good long term results (still good 5-6 years later when I traded the RV)
There is also an epoxy called "Git Rot" that has a good reputation, but-I've never used it.