Others on this forum may have a better idea. Our longest
boondocking streak was last year - 17 days. Maybe used 1/2 a tank and that was for running the fridge, plus cooking. We have the "standard" barbecue grill sized tank. On that 17 day streak we also used our free standing oversized 100w
solar panel with our puny 38 amp hour
battery for phone and tablet charging,
lights and LP detector.
So if you are planning to primarily boondock, probably want to move up to a standard barbecue sized propane tank, or two, or do what one
Casita owner does: 2 half sized propane tanks.