Place onions in crockpot. Trim away any fat that might be present on the brisket. If needed, cut brisket to fit into crockpot; place on top of onions. In a bowl, combine apple juice, sugar, orange peel, mustard, and cloves; pour over brisket. Place cabbage on top of brisket. Cover; cook on low setting for 10 to 12 hours or high setting for 5 6 hours.