Prepare campfire or grill for low heat. Cut a thin slice off top of bread loaf. Hollow out bottom of loaf, leaving a 1/2-in.-thick shell (save removed bread for another use). Spread dressing on inside of hollowed loaf and under the top of the bread. Layer with cheddar, ham, provolone and turkey. Replace top. Place on a piece of heavy-duty foil (about 24×18 in.). Brush loaf with butter. Fold foil edges over top, crimping to seal.
Cook over campfire or grill until heated through, 25-30 minutes. Let stand 15 minutes before removing foil. Cut into wedges.