Hi Chris,

You're on target with the isolator switch. I would think you'd want the battery in question to be a 12 volt (assuming your Econoline is a 12v system, which it pretty much must be, absent some large scale mods). You also want it to be a heavy-duty deep-cycle battery, such as are used to power fishing boat trolling motors and non-engine electronics. The heavy plates in a deep cycle battery give it some durability over automotive starting batteries and the deep cycle itself is designed for multiple deep discharges and recharges, unlike an automotive battery. Lastly, you probably want a 27 series case, that being substantially larger than a normal automotive 24 series case.

Marine suppliers such as Perko make isolator switches, and innumerable websites can provide wiring/rigging instructions.

I imagine much discussion of "house batteries" can be found on truck camper or other RV websites.

I see no problem with fumes on recharge so long as the battery is well-ventilated.

Foy