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. It should pull right off after you get some momentum.
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. Make sure the foil is longer than the rack.
Spray the outside of the rack of ribs with oil spray, then massage dry rub into each side of the ribs.
Cover the ribs with the foil and wrap tightly then store in the refrigerator for at least 6 hours or overnight.
Preheat the oven to 300 degrees F.
Bake ribs for 2 ½ hours. Check to see if they are incredibly tender. If not, leave covered and allow to bake an additional 30-45 minutes. The ribs should have an internal temperature of 145°F.
Drain the excess fat from the ribs, then apply BBQ sauce to both sides.
Turn your oven on to broil and allow the sauce to stick to the ribs, then remove.