You can go to just about any camper RV store and they sell everything you need there. Personally I wouldn't go that route. I've seen cool dual battery setups in the Quadratec and 4WD Hardware catalogs that I'd go with. They have the dual tray, red top gel cell batteries, and cables. This application is used for Jeeps that have a lot of high amp lights and use their winches. More cranking amps and amphours.
85 CJ7 4.0L/SM465/Dana300/AMC20/Dana30, MPFI,154K miles - 33" 12.5's Pro Comp MT's, one piece axles, Detroit Softlocker rear, Lock Rite front, Warn Hubs, 4.56 R&P, 4" BDS lift, Warn x8000i, Warn winch guard, Hi-Lift, Tuffy console, Four X Dr. rocker guards, Rock Hard sport cage, Kilby OBA with 1.75 gal tank and York 10.3cc compressor, Tube fenders by GenRight Offroad, Fabricated rear bumper and tire carrier.