Cover beans in a large sauce pan with about 5 cups of water. Bring to a boil and cook 30 minutes. Drain the water off. Put 1/2 the bacon and onion in the bottom of the slow cooker. Mix all the other ingredients (except beans, bacon and onion) well. Mix beans and sauce together and pour into the slow cooker. Top with the remaining half of the bacon and onion. Cover beans with hot water (just). Cook, covered, on low 4 hours. Remove 1 cup of beans and mash them. Stir them back in to the beans. Cook, covered, another 3-4 hours on low. Make sure the beans are always just covered with water.