Properly rinse ribs and pat dry with paper towels. Turn the rack of ribs bone side up. Using a sharp small knife, slip it between the membrane and the bone then remove the membrane.

In a plastic bag, shake together brown sugar, onion powder, garlic powder, cajun seasoning, black pepper, smoked paprika, kosher salt, cumin, chili powder, mustard powder and cayenne pepper until combined.

Line a large baking sheet with non-stick foil and lay one of the racks of rib on top. Spray the outside of the rack with oil spray and massage the dry rub into each side. Cover with foil and refrigerate for at least 6 hours or overnight.

Oil the grill grates, place the ribs bone side down over indirect heat, and grill covered for 1.5 hours. Turn and grill for another 1.5 hours, checking periodically. After 3 hours, they should be tender, and if not, continue for 30 more minutes.

Transfer to direct heat, brush with BBQ sauce on both sides, and grill uncovered for 5-10 minutes before removing.

Preheat the oven to 300°F. Bake ribs for 2.5 hours, then check for tenderness. If not tender, bake for an additional 30-45 minutes.

Drain excess fat from the ribs and apply BBQ sauce to both sides. Turn the oven on to broil and allow the sauce to stick before serving.