Rub ribs with a blend of the BBQ rub and brown sugar, making sure to cover all surfaces evenly. Smoke until cooked (approximately 2 hours with low heat). Cut ribs into 3-bone sections and place in a roasting pan. Cover with BBQ sauce and watermelon cubes. Wrap pan tightly with foil and braise in a 300 degree oven for 1.5 - 2 hours until the meat is falling off the bone. Serve warm.