The best thing to start with is to replicate what you have with new wood.
The wall frame of a typical RV is attached onto the subfloor and may even be installed on top of the floor covering (vinyl, carpet). If there has been water into the interior, you can bet that the walls have some damage, also. There may even be some floor damage. there may also be rafter damage like rotted ends of rafters or separation of roof rafter pieces.
After you remove all the appliances, the built-in fixtures, and the wall/ceiling paneling, you will have a real good idea of what needs replacing. Typically, roof rafters are attached onto the wall frame top-plate. This means you will want to repair any wall frames and then repair the roof. The subfloor can be repaired by cutting close to the wall and then chiseling out the remainder underneath the wall. A new floor sheathing piece can then be slid under the wall.
Look at the thread in my signature line, "The Cowboy/Hilton". It is all pictured and discussed in that thread.
