HELP fixing roof on a 2001 shamrock

[Keltner001]

First off we are new to the RV lifestyle, so any help would be greatly appreciated.Here is the problem we purchased a 2001 shamrock TT that had a leaky roof and got down into the floor and caused a soft spot in front of the door. The roof is 1/4" luan then 1and 1/4" styrofoam then an outer layer of 1/4"luan then the rubber roof coating. My question is when i remove the rubber will i be able to replace the outer luan and the styrofoam and any interior pieces or are they are glued as one piece. I have experience in cunstruction but never on an rv. as for the floor would I be better off trying to cut out the bad and replace it or take up the flooring to let the wood dry out and the put 3/8" plywood over the old floor and recover any help would be appreciated.

Thanks, Kevin