Unless he can find someone with the exact same model and year who has taken it apart, he's just gonna have to start poking around everywhere to see what is what. I had a 2007 Trail-Lite and I took off every panel that I could to see where and how it was put together. I also went online and printed out every manual for all the appliances, pump, radio, etc. and made my own manual. Most of the time, everything is pretty straight forward and can be fixed or replaced with standard hardware.
Good luck.
Kip
2015 Skyline Dart 214RB
2018 Silverado Double Cab 4x4
Andersen Hitch