Combine dry sherry, vinegar, teriyaki sauce, garlic, onion and brown sugar in a large, shallow dish. Place chicken in dish turning once in marinade. Cover and refrigerate several hours or overnight, turning chicken occasionally.
Prepare wood and charcoal fire in smoker. Place wood chips on coals. Place water pan in smoker, and pour in marinade; finish filling with water.
Spray grill rack with oil. Place chickens on the grill rack. Insert meat thermometer, making sure it does not touch bone (or plan to use an instant-read thermometer instead).
Cover with smoker lid; cook 3 1/2 to 4 1/2 hours or until meat thermometer reads 185°F degrees. Refill water pan and add charcoal as needed.
Yield: 15 to 20 servings.
