Championship BBQ.TV has a nice "how to bbq" video for preparing pork butts for smoking in the Weber Smokey Mountain.
When you place the bbq rub on the pork butt, I wouldn't waste too much time putting rub on the bottom side (fat side) of the butts. Most of the fat will render out when cooking, so there's little use in putting rub on the fat cap.
The video is a testament to the capabilities of the WSM and how it will perform in cold weather.
When I prepare pork butts I prefer to wrap the pork in aluminum foil when the butts reach an internal temperature of 160-165 degrees. This will reduce the amount of dark black coloring on the outside of the pork butts.
I hope you enjoy it.