We recently purchased a 2002 Holiday Rambler Presidential fiver and have completely remodeled it. I purposely wanted this one so that I wouldn't feel guilty taking everything out and decorating it the...
Is he sure it is rot, and is he sure it leaked? Some roofs are thin OSB, and it can break down, and be soft.
This is not something that can be repaired from the inside. If you are handy with tools and carpentry you can likely replace the roof for about $4,000.
Is there a roof vent near the area, you may be able to see into the roof structure and see how much damage there is.