In a spice grinder, finely grind the kosher salt. Transfer to a jar with a tight-fitting lid. Add the rest of the rub ingredients; shake to blend.
Place the ribs, bone side up, on a work surface. Grab a corner of the thin, shiny membrane that covers the ribs; peel off and discard. Sprinkle the ribs all over with 3 tbsp. rub; refrigerate. Prepare your grill
Place the ribs, bone side down, on the top rack over the drip pan. Cover, maintaining the heat between 210 degrees and 230 degrees . Spray with apple juice and sprinkle with the rub every 40 minutes. Cook until the meat is tender and the racks bend easily, about 2 hours. For a charcoal grill, when the temperature drops below 210 degrees (after about 1 hour), prepare more briquettes. Transfer the rack with the ribs to a work surface. Arrange the briquettes around the drip pan; scatter with the remaining 2 cups wood chips. Return the rack and ribs to the grill. For a gas grill, after about 1 hour, transfer the rack with the ribs to a work surface. Add the remaining 2 cups wood chips to the loaf pan. Return the rack and ribs to the grill.
About 10 minutes before the ribs are done, brush with 1/4 barbecue cup sauce. When finished, transfer ribs to a plate, brush with 1/4 cup more sauce. Dust with more rub. Cut between the bones; serve with more sauce.