Having lived for a time in the tropics of Australia and seeing cameras and other stuff literally falling apart with humidity I did some investigation way back then. I used ziplock plastic bags as a necessity whenever outside in bad conditions, which is humidity above 90%, that was a help and hopefully one could either find somewhere with refrigeration air conditioning to de-humidify my cameras, which at the time were small regional shopping centres.
In the mid to late seventies an Australian company started supplying humidity boxes, which were basically a cabinet with seals, an hygrometer attached somewhere and hooked up to a simple tungsten lamp which went on when the humidity went up. With trial and error I was able to get it stabilise around the 35% mark, which seemed about right.
Whatever the supposed correct storage humidity factor is, around 35% worked quite well for me when living in a tropical environment, which was Darwin in Australia, where one is about 12º from the equator, where during the wet season, you can literally see water running down the inside walls of buildings.
There is a fair latitude with humidity, but I certainly have never had things growing when the humidity has been kept around that level.
This is sort of like what I had in the top end of OZ back then.
http://www.ebay.com.au/itm/48L-Digi...r-Lens-Camera-equipment-storage-/370599891984
It is relatively easy to build or adapt an existing cabinet to store stuff. I have thought something very easy would be to find a cabinet, maybe an Ikea type, add seals on the door then run a small tungsten lamp on a timer that switched on and off over a continuous cycle. Slightly more complicated would be to have the light turned on and off with a link to an hygrometer.
Mick.