I have smoked about 5 Boston butts so far. They have all been about 7-8 lbs. I am using a charcoal vertical smoker. I have had a very hard time keeping the outside from drying out. Is this normal. I have not been wrapping the shoulder in foil and I want to avoid this because I like the bark. I have tried to keep the smoker between 200-250 degrees. What am I doing wrong? Any help would be great. Thanks.