Dinolan - I take it you are only interested in insulating the storage room since it will be kept at 55 degrees and 70% humidity and the making area will be more or less room temperature. I'm a little out of my expertise here, but I don't think the humidity in the storage area will condense at that low temperature - it's warm moist air that gives up its moisture when it hits a cool surface. So I believe the barrier on the warm side is what is needed. However, to hedge your bets, I still suggest rigid foam on the joists to provide a barrier to both sides, with no fiberglass to worry about.
I wouldn't worry about any moisture created in your making area - that will simply migrate through to the upper living area at relatively the same temperature. You will, however, face the same problem on your walls of the storage area.
I must say again that I am certainly no expert at this and you will probably benefit from talking to someone who has actually done this, as I believe you intend to do.