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.