If you're fussy, the main breaker box has to be within 18" of where the shore power enters.
I'm using a wire called MC-lite for 120vac. It is THHN wire inside alumuminum armor, with a mylar wrap. What I like about it is:
1. It's cheap (12-2 w/ground) $28/100 ft
2. It has a ground wire
3. It fits through a 1/2" hole
I'm also using shallow blue plastic junction boxes for wiring. They are 1 1/4" deep and fit inside the wall. They cost $0.75 each.
For 12vdc I think stranded wire is the best option.