In a small skillet heat margarine or butter over medium heat until melted. Add green pepper and onion. Cook over medium heat about 5 minutes or until tender. Stir in brown sugar, mustard, and caraway seed. Add sauerkraut; toss to mix. Tear off a 36x18-inch piece of heavy foil. Fold in half to make a double thickness of foil that measures 18x18 inches. Place sauerkraut mixture in center of foil. Bring up two opposite edges of foil and seal with double fold. Then fold remaining ends to completely enclose sauerkraut mixture, leaving space for steam to build. Prick the bratwurst in several places with a fork or the tip of a sharp knife.
Arrange preheated coals around a drip pan in a covered grill. Test for medium heat above the pan. Place bratwurst and the foil packet on grill over pan. Cover and grill for 20 to 25 minutes or until bratwurst juices run clear, turning bratwurst over once. To serve, toast cut sides of buns on grill. Serve bratwurst in the buns and top with sauerkraut mixture. Makes 6 servings.