Simple, one is a work car and what I can't scrounge for nothing, don't get fitted.

. i also tow the van with about 4 other vehicles, so I'm not going to the trouble of doing anything with these - the fridge stays off when on the move. Add to that I'm a lazy Electrican that understands what sort of current draw things have, and always seem to make it work.
What may surprise some is that even though I do high level engine and generator control for a living, programming PLC's, Microprocessors, etc that my battery setups with my vehicles and van are all very simple - solar panel permanently connected to the batteries, those batteries connected to the towing vehicle batteries, a $3 voltmeter and that's it.
Simple in both design and practice - and works great.
Battery isolaters, DCDC chargers, expensive power management - forget it.

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