120, 150, 250 gal sizes how long does wood burn in them and are you messing with it a lot to keep it constant?
Can you set your temp then just let her go and not mess with it much?
here is a picture of my smoker. I really don't know how it would compare as gallon size. Every smoke is differant, every piece of wood is differant, then there is outside temps, wind, ect. Lots of variables. I can tell you on a good day I can go 3 to 4 hours without adding any wood to keep the temps constant. on a bad day it can run every 45 minutes to an hour. hope this helps.