OK, it seems I'm not being clear in describing my need here. Let's try it this way...
Assume the MH is not in the picture... just me, my SUV, and the portable/mobile fridge/freezer. I have a lighter-type plug in the cargo section which the portable will plug into, and it will run the cooler no problem while the engine is running. When the engine is NOT running, I could power the cooler via the plug, and the cooler has a battery protection system which shuts down the power draw when the battery gets to minimum SOC. In this case, the portable will keep things cool or frozen, losing about 1 degree per hour.
My goal here is to set up a separate battery from which the cooler can be powered, and, to recharge the battery, I would employ a portable solar panel(s) with sufficient capacity to recharge the battery everything's attached to. If it's relatively easy to do so, perhaps a system which ties this independent battery to the alternator so that when the car is running, it will also charge the independent battery might also be worth considering...
That help?
