Defrost the roast if frozen. Sprinkle on rub. Rewrap and put in refrigerator for several hours (preferably overnight). When ready to smoke, take out of refrigerator, sprinkle on more rub, and let it sit for an hour.
Get smoker ready and up to 200F. Smoke (I use hickory or mesquite) for about 1 hour to 1.5 hours per pound. Take off, let rest for fifteen minutes, slice, and eat up.
1/4 cup ground black pepper
1/4 cup paprika
1/4 cup corn sugar (get at beer supply store)
2 tablespoons salt
2 teaspoons dry mustard
1 teaspoon cayenne pepper -- ground