Let me fill you in on some Stumps cooking thoughts. I have a 223 and I would suggest using plenty-o-foil or pans, When you load that thing up with a bunch of butts you run a serious risk of flare up. Regardless of how may butts you place in the smoker at a time, put some pans underneath the butts to capture the massive amount of grease that will generate. That said, those pans will block a lot of the heat and you will drive yourself crazy with hitting your target temp. Then if you try to stoke up the fire, you run an even greater risk of flare-up.
My suggestion to you would be to start a bunch of the butts in the smoker and remove half of them once you wrap and place them in your kitchen oven, which should also accommodate four per rack. Place them in foil pans as well.
Get proper separation between the butts and they will cook evenly and efficiently, if you don't get spacing you will cook for twice the time you would cook for just one. Also do not waste your time opening the smoker. Just stick a probe into the butt nearest the hottest part of the cooker. Also, there is no need to mist the butts with apple juice or anything like that, that Stumps cooks very moist.
Just so you know, I cooked three butts last week and they create quite the mess. Therefore place as much foil as possible in the bottom of the smoker which can also be changed out as you cook. Do this stuff and thank me later.