In a small bowl mix the rub ingredients.
Using a dull knife, slide the tip under the membrane covering the back of each rack of ribs. Lift and loosen the membrane until it breaks, then grab a corner of it with a paper towel and pull it off. Season the racks all over, putting more of the rub on the meaty sides than the bone sides. Arrange the racks in a rib rack, with all the racks facing the same direction. Allow the racks to stand at room temperature for about 30 minutes, or until the surface looks moist, before grilling.
Fill a chimney starter to the rim with charcoal and burn the charcoal until it is lightly covered with ash. Spread the charcoal in a tightly packed, single layer across one-third of the charcoal grate. Place a large disposable drip pan on the empty side of the charcoal grate. Fill the pan about halfway with warm water. Let the coals burn down to low heat (250° to 300°F). Leave all the vents open.
When the fire has burned down to low heat, add two hickory wood chunks to the charcoal. Put the cooking grate in place. Place the rib rack over indirect low heat (over the drip pan) as far from the coals as possible, with the bone sides facing toward the charcoal. Close the lid. Close the top vent about halfway. Let the racks cook for 1 hour. During that time, maintain the temperature between 250° to 300°F by opening and closing the top vent. Meanwhile, make the sauce and the mop.
In a small saucepan mix the barbecue sauce ingredients. Simmer for a few minutes over medium heat, and then remove the saucepan from the heat.
In another small saucepan mix the mop ingredients. Simmer for a few minutes over medium heat to melt the butter, and then remove the saucepan from the heat.
After the first hour of cooking, add 8 to 10 unlit charcoal briquettes and the remaining two wood chunks to the fire. At the same time, lightly baste the racks with some of the mop. Leaving the lid off for a few minutes while you baste the ribs will help the new briquettes to light. Close the lid and cook for another hour. During that time, maintain the temperature of the grill between 250° to 300°F by opening and closing the top vent.
After 2 hours of cooking, add 8 to 10 unlit charcoal briquettes to the fire. Remove the racks from the rib rack, spread them out on clean work area, and baste them thoroughly with some mop. Put them back in the rib rack, again all facing the same direction, but this time turned over so that the ends facing down earlier are now facing up. Also position any racks that appear to be cooking faster than others toward the back of the rib rack, farthest from the charcoal. Let the ribs cook for a third hour. During that time, maintain the temperature between 250° to 300°F by opening and closing the top vent.
After 3 hours of cooking, check if any rack is ready to come off the grill. They are done when the meat has shrunk back from most of the bones by ¼ inch or more. When you lift a rack by picking up one end with tongs, bone side up, the rack should bend in the middle and the meat should tear easily. If the meat does not tear easily, continue to cook the racks. The total cooking time could be anywhere between 3 to 4 hours. Not all racks will cook in same amount of time. Lightly brush the cooked racks with some sauce and, if desired for crispiness, cook them over direct heat for a few minutes. Transfer to a sheet pan and tightly cover with aluminum foil. Let rest for 10 to 15 minutes before serving. Serve warm with the remaining sauce on the side.