Like I always said, just take them out and wear them!
Ah, the
BEST way to enjoy a G!
I know every g-shockaholic frets over their babies, me included, but honestly, just wear the things. I won't keep them exposed to direct sunlight when not on my wrist and I don't even get near sunblock or bug lotions when wearing them, but other then that I just wear them when I want to. The only exception I make to that policy are with my vintage pieces. Those I do wear, but sparingly. I also don't buy any model with white or jelly resin because since I only buy what I will wear, and since those two cases are specially prone to get stained, I just don't buy them.
But about humidity. It also can play a role in accelerating the natural decay of PU resin, but it's much less important then UV radiation. However, with older models the ideal storing place would be a dark, dry and cool place. Modern resin is different from the initial formula, so we can expect a much longer life expectancy, and if you don't abuse your G it will surely last a
loooooong time.