Remember that one often ends up adding gadgetry over time, and being able to get wires from cabinet to cabinet afterward is very handy. Consider using some sort of raceway/conduit to make this a simpler task. If the shell is off (or even just the bellypan), some plastic flex routed under the floor will make subsequent additions easier.
If you're going with LEDs, consider using lighter wires for lighting circuits w/ fuses to match. Anything driving motors, etc. will be regular size, of course.
Chafe/penetration damage is a real problem over the long haul; protectig and restraining wires will help prevent problems down the road.
Airstream often left 12V
connections in cabinets w/ simple crimped wire nuts. Consider using plastic boxes to help protect such wires and joints. Of course, no connections where you cannot get at them easily!
All 120V wiring needs to be done to code.
If you're planning an inverter, that needs to be next to the batteries. If solar is in your future, plan for that now, too.