What they said is true. For most of the house wiring they hand a guy a coil of wire and say "Go!" Codes have to be followed, but that doesn't mean much. The plumbing was designed a probably IAPMO approved, but that is also a poor bet.
So, make them yourself.
Get a notebook and some page protectors.
Trace the plumbing. Draw pictures, no one will grade them.
Get a wire tracker and track as much as you can or at least take a day and make a house fuse/breaker diagram. If you do that now, you will have it when you need it. Nothing ever breaks when you are along side in nice weather.
Build these resources now.
This is the advice that I used to give to new boat owners before the depression shut us down. Sometimes I got hired to do this, but usually as a part of a damage recovery.
(Says the guy that bought a coach that has all this from the factory.)
Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.