Really nice to meet a knowledgeable person here!

I will do some calculations about the gel drier system you describe when I have some time. I have worked with saturated salt solution humidity standards in a past project and need to revive some of that knowledge.

As to the vaccum unit, I made a homebrew one using a thick-walled aluminium soup kettle and a 1" thick perspex lid with gasket and taps/guages. Basic, but it works like a charm using an external dual diaphramg pump and a silcone heater mat+control around the kettle. The pump was the most expensive part at about 140 euro's.

I would be very interested in learnign from your experience. Please keep up the dialogue!