Consider this way. Not saying it is the only way, but yields fantastic spares, although I've only done one slab per cook. Put a chimney full of unlit on one side and top with ~6 lit. Put a whole untrimmed slab bone side down flat opposite the coals over a piece of foil on the charcoal grate to catch grease. Cook at 350-375, 3 hours. During the last 10 minutes, put the slab over the coals turning a few times. Yields juicy ribs with a nice crust