Remove thin membrane from back of each slab by slicing into it and then pulling it off. (This will make ribs more tender.) Generously apply Rib Dry Rub on both sides of ribs, pressing gently to adhere.
Light one side of grill, heating to 250° (low) heat; leave other side unlit. Place slabs, meat sides up, over unlit side, and grill, covered with grill lid, 2 hours and 15 minutes, maintaining temperature inside grill between 225° and 250°.
Remove slabs from grill. Place each slab, meat side down, on a large piece of heavy-duty aluminum foil. (Foil should be large enough to completely wrap slab.) Pour 1/2 cup of Rib Liquid Seasoning over each slab. Tightly wrap each slab in foil. Return slabs to unlit side of grill. Grill, covered with grill lid, 1 hour.
Remove slabs; unwrap and discard foil. Brush Sweet Barbecue Glaze on both sides of slabs. Grill slabs, covered with grill lid, on unlit side of grill 15 minutes or until caramelized.