Ryan,
I installed a middle rack in my 22" just for this reason. I dropped the lower rack a few inches first so that each layer could comfortably hold 4 butts without hitting the rack above.
Back in April I did 12x 10# butts. It’s a pretty tight fit, and it’s a LOT of meat.
Here are some things I learned when doing 12.
First, I do not use water, I use a foiled pan. Make sure to leave room in your pain for grease, because there is going to be a lot of it!
I would suggest only loading the bottom & middle racks if you plan on lifting the middle section when firing the smoker. Even then, it takes a bit of muscle. After the smoker is going, even with handles, I wouldn't suggest trying to move 100+ lbs of meat on a hot smoker, with a bunch of grease waiting to spill.
If you use a meat thermo, just put one per rack. I used them originally, but for my last 9 butt cook I went with a set of skewers to test.
I normally cook my butts in the 260 range. These cooked at 230 because the temp did not want to come up, so they took a little longer than I am used to at 260ish. Looking back at old cooks that I used to do around 230, they took a similar amount of time.
Getting to 230 took 1.5 hours. Normally I am up to 260 in 30-40 minutes with a lot of meat. I started with 3/4 lit; I would definitely go with 1 full chimney lit. I attempted to get up to temp faster by cracking the door, which isn’t so easy on the 22. A couple weeks ago I cooked 9 butts and cracked the lid instead, got to temp MUCH faster. Because of this I want to install a second top vent on my 22 since I will use it a lot for these large cooks.
Neither on my 12 butt or my 9 butt cook did I initially rotate or move the butts. On the 12 butt cook, the top 4 butts were not close to done when the bottom 8 were done. On my 9 butt cook, the top 3 were closer this time, but still not really close to the bottom 6 once they were done. On the 12 butt, the top ones took 2-3 hours after the bottoms ones were done. On the 9 butt, they took 1-2 hours more than the bottom ones. I would suggest putting your smaller butts on top.
I used more charcoal than normal because I used a lot of it getting up to temp. I think a full lit chimney at first would help this, but you are still going to use a little more. For the 12 butt cook, I used a 23 lb bag of blue K in the ring, plus what went in the chimney. I then had to add a couple handfuls towards the end finishing up the final 4. Ditto for the 9 butt cook.
I am also going to get a clay saucer to absorb some of the initial heat instead of just going with an empty foiled pan.
Very important, although I did not learn it doing these larger cooks. Make sure to close your bottom vents before you remove the lid to remove the butts. It will take awhile to test all the butts and to get them off the smoker. Your temp will soar if you keep the bottom vents open. Wearing hi temp food gloves will speed up removal. I use Steven Raichlan’s. They originally came in an off white, which mine got trashed quickly Just got a new pair in dark gray and they clean up much better.
If you have any other questions, just let me know.