Preheat the oven to 300 degrees F and line a large baking sheet with a piece of aluminum foil large enough to cover the pan twice (you will be folding this over the ribs and sealing.)
Place the ribs on the prepared baking sheet in 1 layer. In a small bowl, combine the Rib Rub, salt, pepper, and celery salt and stir to combine. Divide the seasoning evenly among both slabs of ribs, coating well on both sides. Fold the sides of the foil over the ribs and seal tightly on all sides. Place the ribs in the oven and bake, undisturbed, for 2 1/2 to 3 hours, or until ribs are very tender.
Remove the ribs from the oven and peel back the foil so that the ribs are exposed. Using a pastry brush or the back of a spoon, coat the racks lightly on the meaty sides with barbecue sauce. Return to the oven until sauce is thickened and lightly browned, about 20 minutes longer. Remove the ribs from the oven and set aside to cool briefly before cutting between the ribs and serving. Serve with more barbecue sauce, if desired.