Sleepy,
My GMC is not my first RV. They are almost alone in information available, but do not be jealous just take the time to do this:
Get the service manual for the chassis.
Get a loose leaf notebook and start today.
Make a page of notes about what you find that was added under the hood and elsewhere to that chassis.
Collect the manufacturer and model of all the stuff inside. Now, get on the web a find everything you can about that stuff download it, print it, punch it and put it in the note book.
Early on, start with the AC breaker box. If the breakers aren't labeled and clear, identify what each does.
Then, do the same with DC house power fuses. The pages for both of these in your notebook will save you immense amounts of grief when you need them. You will need them.
When you are working on things, make pictures (take pictures) and notes about what you find.
We have had this coach only 13 years. I recently had to go back to something I had done when we first owned it. I'm glad I had notes. I may be retired, but I am not that old.
Matt