Sounds like a great plan, Lance! You've definitely been studying us! lol. I'm confident you'll like Dave's rub on the butt - it's great. I fill my loaf pan about 3/4 full, but 1/2 will probably be fine. It shouldn't dry out. Also, put your box temp probe on the same level as your meat (btw, put your meat as high as possible - the heat is more stable at the top), but not too close to the meat (cooling effect). Keep the probe at least 2-3 inches away. You're also right about meat probe placement; make sure it isn't touching the bone. Be ready for the "stall," and embrace it! This is when all that fat and connective tissue in the butt is rendering, and the real tenderizing is going on! No matter how long it takes, just let it ride! Once I get through the stall, and the temp starts to climb, I usually bump the temp to 235-240. The higher temp, post-stall, won't hurt a thing, and will speed things up a bit.
Good luck, and be sure to post some pics!