Sorry to say but there are not many cases of plumbing diagrams being available for current models and even fewer for 29 year old models. Just like plumbing in a house, the lines are usually made so they use the least amount of piping. Just like someone who bought a new trailer, you will have to trace the lines and where they go with no idea of where to begin. What type of lines are you trying to fix? Also, what do you think caused it? If it was frozen then every bit of piping is suspect along with valves and fixtures. If you think it is just the obvious break, go directly above the break inside. Chances are it goes straight up to a fixture. Not usually a lot of wasted length in an rv plumbing system.
