Remove membrane from ribs by sliding butter knife underneath and peeling back the membrane on the back. Season ribs all over with rub, concentrating on the meatier portions.
Cook ribs over indirect heat (250°F-300°F) for 3-to-4 hours. If a smoky flavor is desired, mesquite, hickory, apple or other fruit wood can be soaked in water and spread in small quantities over the hot coals periodically during the cooking.
After the 3-to-4 hours of slow barbequing, arrange ribs on a shallow-sided disposable aluminum pan and mop them on both sides with the mixture.
Cook for 1 more hour. Mop ribs again, then turn them over. Baste the ribs and keep grill at even temperature.
Baste on both sides with your BBQ sauce of choice, sprinkle lightly with garlic and onion powder, and wrap each rack of ribs in heavy-duty aluminum foil. Allow ribs to remain in foil for 30 minutes.
When ribs are done, the meat will have shrunken away from the ends of the bone by approximately 1/4-inch or so.