First off, I wouldn't recommend that anyone attempt installing an electrical sub panel, if they don't have some prior experience.
That said, I would be glad to lend some design assistance and possibly help you with your install if Im able.
From your description, I can't really picture what you already have in place, perhaps you can post photos?
Cheers, and good luck!
David D. Bosley
Call Sign: KD0DHK COHVCO: #4409 AMA #222838
1997 White Toyota Tacoma (aka TruckWagon)
2007 Blue Suzuki DR 650 (aka TigerCub)
2002 Roulette Green Triumph Tiger 955i
2003 Silver Triumph Tiger 955 (RIP)