When you purhase a new motor home it comes with a fairly comprehensive package of manuals covering "most" of what you are looking for. When you purchase used that package may or may not still be there. The two things I can think of that you can do now is:
1. Go to rallies. They always have informative seminars you can learn from, plus the attendees themselves are a wealth of knowledge.
2. Go to the manufacturers websites of the appliances you are interested in. Many of those contain helpful information
