Hi,   

After running out of propane years ago with 3 young children in our pop-up with sleet/snow in the process and a hefty wind on a Sunday morning in the UP of Michigan in the late 1980's, and nothing was open, I vowed I would always carry a spare tank, . . . . and I do.  We carry 2 20lb tanks on the front of our 177.  As far as how long they last, it all depends on how warm you keep your pod during the day and night, cooking doesn't use very much.  We camp about 30 days/year and can usually get 22-25 days out of one tank, again it depends a lot on outside temps, is it going to be in the 30's or 50's at night, that is huge.  Do you want it like Florida inside at night-time or are you going to keep it at 55 degrees?  We tend  to be a bit on the soft side and like to keep it around 58 -60 at night even when the temps are in the 30's or 40's during the night.  During the day, since we usually are out hiking, the furnace is turned OFF.  And then the other thing to consider is how you fill your tank.  Do you not mind getting ripped off by Blue Rhino (getting a full tank that is only 75% full) or do you take it to a hardware store or similar where you can actually get it filled to the max?  Lot of discussion on this elsewhere on this forum.