Now THIS is a question of curiosity that may have the interest of some folks. We often compare mileage and to some extent electric power consumption,... but what of propane??? It's something I'd bet many have little concern of, since most seasonal and summer use is pretty minimal, even for me as a full-time year-around live aboard.
My "upstairs apartment on wheels" is actually quite comparable to my previous "rolling cottage/cabin" during summer months,... and very minimal in propane use really. But this time of year can be quite different, even the occasional weekend venture may need a bit more consideration of "jus how much propane will I be using?" "Will I have enough??" And Oz stated, it can be quite dependent on your appliances and their use, as ones level of comfort and convenience can be quite different from another's. And staying warm during winter outings can be pretty important!
FYI,... 1gal propane=4.24lbs, do any math ya need from here.
But I might offer an "extreme" of sorts. My Cruise Air II has a 100lb tank, and holds 22.5gal at 80%. Equipped with 2 furnaces (of which I only really use one), a 4-burner stove I occasionally use, and a typical hot-water heater that I only turn on when I anticipate the need for a shower, morning wash-up, dishes or whatever. I no longer have a propane refrigerator, but when I did, I found it to be minimal in propane use, even in summer. Heating for comfort is the biggest consumer of propane. During the cool late autumn season, when sunset brings cooler evenings and even colder nights,... my tank would last about 10days to 2wks or so (about 1.5-2gal a day). This is when the furnace begins to come into frequent use.
Currently,... the past 6wks have seen temps constantly below freezing, and frequently near zero!!!! My logs show that I use about 2.5gal of propane a day. I'm VERY comfortable, and other than a short exposed waste outlet, nothing has frozen up yet! Under such extreme conditions, I would expect your 80lbs to last ME about a week max!!!
What of others here?