The biggest enemy is moisture. The one I had stored here was allowed to cool way down below freezing which meant there was minimal moisture left in the air. Then I made sure it was full of trans fluid as described in the previous posting. After that I double plastic bagged it and pumped all of air possible out of the bags. Then the bags were sealed and the trans was stored inside at a near constant 65 degrees F. This prevented moisture from condensing on the inside parts which would normally occur during seasonal cold to warm temperature changes.

Without resorting to unrealistic and/or prohibitively costly measures, I'd have to submerge the whole tranny in atf within a container that could be sealed after displacing the air.