Regarding my original post - I have found limited solutions. Last night I put in a 13.7 pound (untrimmed) brisket at about 11 PM. I had bought two bags of Royal Oak briquettes and a bag of RO lump. I used a whole bag of briquettes initially (about 3 chimneys) including the lit one I put on top. I boiled the water (probably not more than half a gallon and put it into my new foiled Brinkmann water pan. Temps initially went up nicely, and at 300 I closed the lower dampers to 1/2 - after less than an hour I was running with everything open trying to get heat again. I checked again at 3:30 AM and temps were 225 or so. At about 7 AM I lit a chimney of Royal Oak lump and dropped it onto the remaining briquettes, then filled the ring to the top with unlit lump. I was able to run till about 2:00 in the afternoon with intermittent fire stirring, adding another scoop or two of lump, and on average I had the lower dampers about 3/4. Once the brisket hit 205 degrees I took it inside and decided to see what would happen with the temp. Having had the top off for a while removing the meat, I initially got over 250 and eventually closed the dampers to 1/4. An hour later I was still almost 250, and then it started to fall. Right now, 5:30, it's still lit with everything open and having stirred the remaining coals, running about 225. And there's still water in the pan, which I've never refilled. It was boiling during the cook, but never ran out.
15 pounds of briquettes and maybe 10 pounds of lump - an expensive way to cook $35 worth of meat. Costco had a Kamado Joe road show right next to the brisket when we went to buy meat last night. I want one. Bad.
Honestly, I'm stumped at this point. Maybe I'm missing something. That sounds like a relatively straight-forward cook, maybe a tiny bit fuel-hungry, but nothing crazy. First off, a WSM has never been a Kamado/BGE nor is it supposed to be. You won't get that level of insulation.
Second off, you said you put the brisket on at 11pm. Let's assume you had the charcoals burning starting at 10? So from 10pm to 5:30pm the next day and STILL running at 225. That's 19.5 hrs worth of coal burning. 25 lbs of coal is certainly not out of the realm of possibilities. On any cook over about 12 hrs, I'm almost certainly going to be going through a whole bag of KBB on my 22", and if I recall from my 18" days, a typical cook on a set of pork butts (22lbs) took up pretty much an entire bag.
Third, you need to clarify some stuff. You say
"at 300 I closed the lower dampers to 1/2 - after less than an hour I was running with everything open trying to get heat again.". What does that mean? What was the temp? Had you opened the lid recently? Did you simply mistake the fire "settling in" for a temp drop? So many different factors.
I'm starting to wonder what your expectations actually are with the WSM? Are you expecting something along the lines of being able to cook multiple briskets on a single bag? Cuz it's not happening. And charcoal is certainly not expensive. You say it's going to get expensive, but I spent under 100 bucks on charcoal this year, and I still have 3 bags of KBB left. I've done probably 25-30 cooks this year, at minimum. Charcoal
IS cheap.
My honest suggestion to you is to join or consult a local BBQ/grilling club and get someone to come do a cook with you, perhaps. If your smoker isn't showing signs of massive leaks, I've really got nothing else to suggest, other than to think maybe you're reacting to rapidly to your smoker and doing things to the dampers that actually harm it, rather than letting it be. It's really hard to say.
