Since he is a truck guy, one way to help sort fuse locations may be to think of what would be on the normal truck chassis before they put a bed or box on the back. Those are often added by the chassis folksand then that stripped chassis is sent to Winnebagoand they add the RV stuff. So if it is something often found on a truck ( horn,lights, turn signal?) it will likely be found in a different box (under hood?) than things like inside lights, vents fans, furnace, microwave, etc. which the RV folks add.
Nothing is totally firm on that but kind of a start.
One of the biggerproblems with RV is the way we tend to use them. With acar, we can keep the battery charged up, even though there are thingslike radio presets, auto doors and ignition things that stay on and can runn the battery down---but not if we drive it every day or so.
But if we have the same drains on the RV and park it for several months, the battery does run down if we don't do something to keep it from happening.
Parking it makes it break down faster than using it every day, so keep those wheels turning!