A guy on another board has a taxidermist friend who gave him the following mixture to tan skins.

2 lbs of salt.
250 grams of Alum. (The Alum is an astringent , topical disinfectant. In any pharmacy store.)
100 milligrams of borax.
2 gallons of water.

-Boil untill everything is melted down.
-Wait until it cools then add 1 tsp of Sulfuric Acid. Rubber Gloves at this point on! (you can get the sulfuric acid in a hardware store that sell plumbing supplies. Its in an industrial strength form. I got a 1 L bottle for $6.oo. You use only one teaspoon per shot. so you good for a while.)
-Make sure all the skins are submerged in the sollution. Put weight if needed.
-Ready in 4 days.
-hang or stretch to dry. ready in 3 or 4 days. Bend the skins to get it soft.

I haven't tried it myself yet but several other folks tried it and seem to like it.

Fatman