I'm a fan of do-it-yourself ... but i'm also a fan of do-it-SAFELY-yourself.
May i suggest finding a "van conversion" or boat up-fitter and "buy an hour" of their time for some hands-on training in safe wiring of moving/vibrating vehicles?
Connections that won't fall apart, grounding considerations, wire choices, etc etc.
A loose wire-nut can lead to fatal errors ... your van metal getting (electrically) "hot" compared to the wet grass you're about to stop onto, or which you are standing on when you insert your (metal) key in the door.
A standard residential electrician might help, but they're not going to be fully aware of, and practiced in, the extra things you have to consider for an RV due to the environment.
As an example, visit that
RV Electric site and click on "open neutral" in the left margin menu. Then read.
All it takes is one can't-really-hold-it screw to lead to "interesting" consequences.
That page is discussing the power kiosk, but there have been a number of forum members who have discovered their commercial RVs were having loose or disconnected wires inside the van where the exterior connection met their major feeds.
--dick
