Prepare a medium hot fire for indirect heat cooking in a covered frill according to manufacturer's instructions. Position rack 4-6 inches from fire. Soak 3 handfuls of hickory chips in water to cover for at least 20 minutes.
Place each slab on a piece of heavy-duty aluminum foil. Sprinkle with 3-4 tablespoons of beer or water. Wrap tightly and place on grill rack. Cover grill, open vents and cook, 45-50 minutes.
Meanwhile, in a saucepan over medium heat, warm oil, add onion and garlic and saute until tender, about 5 minutes. Stir in tomato sauce, ketchup, vinegar, orange juice, brown sugar, mustard, Worchestshire, salt and pepper. Bring to a boil, reduce heat to low, and cook until thick, about 15 minutes.
Sprinkle soaked hickory chips over hot coals. Unwrap ribs, return to grill rack, and cover grill, partially closing the vents. Grill turning occasionally, until tender, 20-25 minutes. During last 10 minutes of grilling, brush ribs with sauce. Transfer ribs to a work surface, cut racks in half, and mop with more sauce. Pass remaining sauce at table.