Electrical system kit for a home built trailer

Start with a main electric panel. Do you expect to be a 50 amp or 30 amp RV?

http://www.bestconverter.com/4000-Series-Compact-Power-Center_c_138.html

Are you going big on solar and battery? Solar is usually separate with panels to the controller and controller direct on the battery. About 100 watts solar for 100 amp/hr battery is a good starting point.