I always see people talking about only having one vent open or two partially open. I run my WSM with all three open, 275 degrees (verified with a Maverick thermometer), and I can run all day on one load. No re-loading charcoal, the hotter temp lets me power the butts through the stall a bit quicker, and I'm a no foiler.
I'm doing two over night tonight and throwing a couple racks of ribs on tomorrow morning, following that all by two more butts once the ribs are off. Should be a loooong 24-36 hours of smoking, but I would imagine that I'll have one full reload and that will be about it.
How did your cook turn out?