I completely agree with Herb. However, if you'd like to get a head start if you can't get together with Greg quickly, posting some pics of your electrical stuff will help. It's probably all centrally located under a couch bed (gaucho) or is on most SMBs.
Also, if you can install a car stereo, then you have a basic grasp of vehicle (DC) electrical systems. Half the battle is won. It's just power and ground wires, and you have an inverter/converter or the like to switch the AC power to DC, or vice versa, or both.
If you start by cranking the van and testing each battery with a digital voltmeter you'll start getting an idea of what is going where and when with the electrical system.
Welcome to the gang, lots of great help here at fantastic rates!