I foil mine around 165*. To make life easier, I place the foil across a disposable pan, then place the butt on it and wrap in up. Gives me handles to hold on to. I'm not a fan of putting the butt in the pan and foiling the pan. I have found that if I use a rub with a good amout of sugar, and make sure I have a good coat when the butt goes into the smoker, I get a great bark, even with foiling. At 190*, I start checking for doneness.
CBJ, 15' custom BBQ trailer with a Backwoods Competitor, Pitts & Spitts off-set, & Santa Maria grill. Ole Hickory CTO, 1 BGE, 2 Weber kettles and 1 Smokey Joe, BWS Chubby, Sonoma gasser, and a BBQ store full of everything BBQ.