John.......are you telling me you have cooked "about" 12 smokes on our WMS and have never had to add any charcoal ? I want to know what kind you use if so.
Secondly, I never mess with the side door. I lift the lid off the cooker, then lift the middle portion off (while it's cool of course) and for 4 butts it's going to burn a long time. My last pork butt took me 20 hours to get the meat to 175 internally. Granted, I did an overnight smoke and had my temp contoller set too low (210). The next morning I bumped it up to 250 to try and get the internal temp up on my pork butt. It was a 9 pound butt, so I loaded up my lower charcoal ring all the way to the top and then added my hardwoods along with that. I did not have an abundance of left over charcoal, but a little. I keep a pair of FABULOUS gloves on hand to mess with the hot smoker during a smoke. I bought them from texasbbqrub.com for $11.00 and free shipping. They are heavy rubber that go almost up to the elbow, but have a nice soft lining inside and they are great.
I hope this helps a little, But I use the Minion Method when cooking. I put in what charcoal I want and I have an old coffee can open on both ends and I set it in the middle of the charcoal grate. I put all the charcoal I want around it and as high as I think I'll needd to cook. I then put a bit more in an upside down chimney and light it and get it really hot. Being very careful and with my heavy gloves on, I remove the can with some pliers and then dump the hot coals into the center of the remainder of the un-lit coals. The hot coals continue to light the outer ones a bit at a time thus giving you a longer burn on your fuel. Hope that makes sense. The charcoal lights a bit at a time from the center outwards and along the way it's also burning the hardwood. You can put some of the hardwood under the charcoal also so it burns during the cook and does not all get burned in the beginning. I'm not sure that is effective, as some mmuch more experienced cookers than me say the meat does not absorb any smoke after about 140 degrees. I dunno.
Good luck, and let me know how you got 12 cooks on one load of charcoal please.