DISCLAIMER: Everything that I am about to say is not personal experience, just what I was told (credibility unknown), but I am about to experience nearly the same issue.
Apparently inside the walls there is basically a wood frame (picture your house framework). If you CAREFULLY remove the aluminum siding and windows you can remove all of the rotten wood and then basically rebuild the wall by re-framing and then installing new plywood. I don't know if the roof is the same way, but shouldn't be too different, if any. This may not be the professional way, but its what the PO of my trailer "say" they did to one of the walls and it doesn't look too bad. I can't even tell unless I am looking for it.
Hope this helps!
P.S. I am going to have to do the same thing with my trailer, 18', where water leaked in near the A/C, but went directly to the door and then down the wall around the door.
Good luck, and I'd love to hear about the results.