Have a 5er,Want to get a used TC for me.What to watch for?

Turbothrust

Do you have any experience repairing a rotten foundation in a fiberglass camper? I recently purchased a used Northern Lite that evidently was owned by one of the many who think they require less maintenance. The floor under the basement on the passenger side is rotten due to water and I am trying to determine how to fix it without gutting the thing.