The important question is "what are you going to be doing"
Are you going during cold weather and need heat, or nice weather without?
Are you just doing weekends, or for weeks at a time?
Are you going into the wilderness, or will you be near town?
Will you use hook-ups and use your electric power, and their showers?
In other words, how much gas will you be using, and how far will you be away from a refill?
On our construction job site during the coldest of the winter, hooked to a 170,000 BTU space heater, one 4-5 gal (30lb?) tank will last quite a long time.