I have had good luck with the wrapping it in foil after it gets to 165. then cooking to 185 let rest for 30 min. I save all the juice and let my guest put it on the pulled pork if they want.
185? I'd let 'er rip till she probes like butter, and 185 isn't gonna be there. I don't pay attention to internal temps with butts, and certainly don't waste expensive foil for a butt till the resting period.
Oh, and 3-4 hours of rest is required (by me) on all butts/picnics.
In regard to cooking temp, I doubt the thermometer in your WSM is showing an accurate reading of what's happening in the center of cooking grate. My guess is it's showing 40-50 degrees lower than grate temp.
I tend to agree with --K--, all that voodoo, foilin, spritzin, moppin', etc, is extending the cook time, which will open the door for dry meat. I like to toss meat on, drink lots of wobbly pops, listen for the meat to quiet down (you can hear it cooking), then start checking for buttah.
Try cooking at 250 for first hour, then ramping up heat to 300. The process is shortened, and that lowers the chances of a dry result. Yeah, I know, the low and slow folks will be sayin "WTF?", but a faster cook will give a chance for a moister result (less time in heat, but higher pressure since you're not peekin.... EVAR).
Fat renders the same at 300 as it does at 225, the only difference is you get more sleep.