I have many years of experience at this sort of cooking during historical reenacting. The one thing I can tell you is never ever hang an empty pot over the fire. It always needs to have some oil, water, milk, or broth in the pot, depending on what you're cooking. Then, when you're done cooking you can clean your pot with soap and water, but after drying you need to put a little oil in the pot and re-hang it over the fire to warm it and spread the oil over the inside of the warmed pot. This will keep your cast iron pot from rusting.