Prepare the ribs and rub: Remove the thin papery skin from the back of ribs by pulling it off in a sheet with your fingers, using the corner of a kitchen towel to gain a secure grip, or with pliers.
Combine the Paprika, Black Pepper, Brown Sugar, Salt, Celery Salt, Cayenne-if using, Garlic Powder, Dry Mustard, and Cumin in a small bowl and whisk to mix. Rub 2/3 of this mixture over the ribs on both sides, then transfer ribs to a roasting pan. Cover and let cure, in the refridgerator, for 4 to 8 hours.
Prepare the mop sauce if using:Mix together Cider Vinegar, Mustard, and Salt in a bowl and set aside.
Set up the grill for indirect grilling and place a large drip pan in the center.
If using a gas grill-Place all of the wood chips in the smoker box and preheat the grill to high; when smoke appears, reduce the heat to medium.
If using a charcoal grill- preheat it to medium.
When ready to cook, if using charcoal grill, toss the wood chips on the coals. Brush and oil the grill grate. Arrange the ribs on the hot grate over the drip pan. Cover the grill and smoke cook the ribs fore 1 hour.
When the ribs have cooked for an hour, uncover the grill and brush the ribs with the mop sauce(if using). Recover the grill and continue cooking the ribs until tender and done, 1/4 to 1/2 hour longer for baby back ribs and 1/2 to 1 hour longer for spare ribs. The ribs are done when the meat is very tender and has shrunk back from the ends of the bones. If using a charcoal grill, you'll need to add 10 to 15 fresh coals to each side after 1 hour. 15 minutes before the ribs are done, season them with the remaining rub, sprinkling it on.
To serve, cut the racks in half or, for a plate-buring effect, just leave them whole.