I have a Coachman Genius 4 berth 1997 model?

I have damp in the corner and have taken the awning rail of to re seal, I found the wood on the front corner is rotten so the screws just pulled out. I have stripped the side seat out and the wall is wet to under the left hand side window. I am having problems because the corner runs in behind the internal bulk under the front windows and it looks like I will have to remove it to replace the rooten battons. Has anyone removed the front bulkhead and how because I can feel a metal frame behind it in the damp corner. I have also noticed that about 3 feet of the floor edge is also loose and the external rail screws can be seen. Looks like the edge batton also rotted but the floor ply seams intack.
Can anybody help if they have had the same problems.