Combine onion rings, soy sauce, and brown sugar. Place in crockpot. Whisk beer, mustard, and caraway seeds together. Place in crockpot and mix with onion mixture. Place brats in crockpot and mix all well. Cover and cook brats 6 hours on low or 3 hours on high. Place brats on platter and keep warm. Stir sauerkraut into onion mixture in crockpot and let sit about 5 minutes, until warm. Strain onion/sauerkraut, (keep liquid). Put all other ingredients in a large bowl. Place brat on a bun and add the rest of the ingredients on top. If there are brats left, place in a container, and add some of the liquid, store in refrigerator.