One thing you don't want to do is use any kind of soap on the cast iron -- It may be absorbed and may affect food taste (I'd rather pee in it than use soap!!).
The Lodge site http://www.lodgemfg.com/
has useful information about the care of cast iron, including this on re-seasoning:
Re-Seasoning your Lodge Cast Iron
While maintaining the seasoning (as in Step 5 above) should keep your Cast Iron in good condition, at some point you may need to repeat the seasoning process. If food sticks to the surface, or you notice a dull, gray color, repeat the seasoning process:
Wash the cookware with hot, soapy water and a stiff brush. (It is okay to use soap this time because you are preparing to re-season the cookware).
Rinse and dry completely.
Apply a thin, even coating of MELTED solid vegetable shortening (or cooking oil of your choice) to the cookware (inside and out).
Place aluminum foil on the bottom rack of the oven to catch any dripping.
Set oven temperature to 350 – 400 degrees F.
Place cookware upside down on the top rack of the oven.
Bake the cookware for at least one hour. After the hour, turn the oven off and let the cookware cool in the oven.
Store the cookware uncovered, in a dry place when cooled.
I have read a long time ago in Yankee Magazine (How-to column by Earl Proulx) that one way to start the re-seasoning process is to put the utensil in a leaf fire (best done in the Fall
, of course, when there are plenty of leaves to burn) and then allow it to cool slowly before adding the shortening or oil. Of course, you would want to vigorously wire brush or sandpaper or whatever the major rust first. A good hot campfire would also work (FullTimers don't have ovens at home for baking the cookware!).
BTW, nothing wrong about cooking with the rust -- Remember when Sun Maid raisins used to advertise that they had a lot of iron in them? It came from being processed in large cast-iron vats -- No iron nowadays because they are using stainless steel vats.
I have the cast aluminum Dutch Oven by GSI (I was trying to keep my Full Timing weight
down) and the care is a lot simpler because the aluminum doesn't rust -- I just wipe out inside of the pot with some paper towels and add some cooking oil.
Here's photo showing my aluminum DO, my single-burner Coleman stove, the bucket it all goes in so it won't tip over and the home-made cover lifter and pot holder -- I can adjust the height of the DO and stove in the bucket by adding wood under the stove -- I do have to keep a watchful eye on it when cooking because there is a lot of heat reflected back on the stove from the bottom of the DO.