setxjohn --
Wife and I bought an '83 25 footer and it's going to need the front half: ceiling, walls and part of the floor replaced due to water damage / leaks.
For the most part, it's rather straightforward (very similar to replacing a subfloor in your home) but, it won't be until you dig in and find the source of the leak(s) before you'll know exactly how difficult it will be.
Once you get started, feel free to take pics and post them here if you have any questions. There's a bunch of knowledgeable folks on these boards who can give seasoned advice and/or give moral support.