I've never brined a butt before, but I do what I call a steam brine in my smoker for butt and they come out great.
Basically I use 1 Webber chimney of coals in my basket and put about 1/2 pan of hot heavily salted water (I use the good sea salt) directly on the coals. I usually make a small circle in the coals so the pan fits nice and snug. I also put some fresh herbs in the water from the garden depending on how I feel that day. Parsley, cilantro, oregano, rosemary or thyme. Once the water gets boiling it sort of steams the meat for about an hour or so putting in a slight hint of the herbs, but more importantly adding moisture back to the meat in preparation for the long smoke yet to come. Since the meat doesn't sit in the water it doesn't give it a salty ham taste, but does give it that extra hint of flavor and moisture.