Preheat your smoker to 225°F. In a small bowl, mix the salt, pepper, paprika, garlic, and onion powder. Coat the tri-tip with the rub. Place the tri-tip on the smoker and cook until a meat thermometer inserted into the thickest part of the meat registers 135°F, 2 to 3 hours.
Remove the tri-tip from the smoker and allow to rest 15 minutes. Thinly slice the meat against the grain. Serve with barbecue sauce.
Makes 8 to 10 servings.