With a 10k btu tube burner in my Smoke Hollow, I have done a couple 16-18hr butt/brisket smokes, along with 3 to 4 BB rib smokes of 6hrs each and still had Lp left for some sausage smokes, which while they're at lower temps they still run 5-6 hrs each. Never really paid any mind to the usage, as I've been very pleased and surprised with the low rate of consumption. That was one of my concerns also, maybe I just got lucky with this unit. Also use Todd's pellet tube and tray, mainly the 5"x8" tray, 18" tube has to lay diagonal on bottom as I guessed wrong of depth when ordering. My smoker is also a double walled unit which helps with heat retention.
Remember if your looking your ain't cooking...
The smoker is model 41170 deluxe, but always keep a spare tank on hand. Hope this helps
Good luck...