I would guess that a fridge can run almost 2 months on 20lb tank. When boondocking my biggest concern would not be the minuscule 12v required for the fridge, but the other parasitic loads most motorhomes have. There are usually several, and added up, they take a toll on the house batteries. Get a voltmeter and check your batteries every day(if possible) to keep an eye on what's going on.
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2016 R-Pod 176T
2002 Avalanche Z71 Tow Veh
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