Mix brown sugar, garlic powder, and cayenne together in bowl. Add salt and pepper if you wish. Rub spice mixture onto ribs, both sides. Wrap ribs in aluminum foil, using two sheets of foil. Place ribs in fridge for at least 24 hours. Remove ribs when ready to prepare and place in oven on warm. (My oven goes from warm to 250degreesF, so I say place on warm, if your oven does have temps. lower than 250degreesF, I would suggest 200degreesF Bake ribs on warm for at least 4 hours, up to 6 hours. Remove ribs, and let them sit in foil, allowing them to cool to almost room temperature. Place ribs on hot fire, and baste with your favorite sauce. Let ribs cook on grill for approx 15 minutes or until hot. Remove ribs and let them rest for approx 10 minutes before serving.