Preheat your smoker for indirect smoking with a temperature of 225°F.
Pat dry the ribs with paper towels to remove excess moisture. Next, remove the membrane from the underside by slide a knife tip beneath to separate it from the meat. Then grasp with paper towel and pull it off. (You may need to do it in multiple pieces.)
In a small bowl, mix the paprika, garlic powder, mustard, salt, pepper and brown sugar.
Rub the ribs on all sides with the seasoning mixture. Then place them bone side down in the smoker to smoke for 3 hours.
Remove the ribs from the smoker. Place each rack on a large piece of aluminum foil. Pour about 1/2 cup of cider vinegar around each rack. Then carefully wrap the ribs as tight as possible without puncturing the foil.
Using oven mitts, carefully place the wrapped ribs back into the smoker for 2 hours more. (During this time the vinegar will steam the ribs and make the bones protrude about a half-inch.)
Remove the ribs to a work surface and unwrap. Brush with the leftover liquid (if any) followed by the BBQ sauce.
Place the ribs back into the smoker for a final hour, or until the sauce has set, about 1 hour (see note).
Remove the ribs and cut into pieces to serve.