I wasn't sure that you were replying to my post, because it's very dry where I live.

But humidity does nothing good for a tire, the "drying out" of a tire's various polymers has nothing to do with H2O and everything to do with ambient levels of smog molecules like ozone which causes visible cracks in tread and the disappearance of sidewall rubber.
We've got some of the highest summertime smog levels here, and an inner tube left exposed can develop catastrophic cracks in just a couple of short months.

H2O can permeate various solid and elastomeric polymers up to surprisingly high percentages (something I learned studying polymers and composites in school), but isn't much responsible for the supple feel of fresh rubber tread or the sidewall rubber coating, or for the appearance or absence of cracks in aged rubber.
Humidity does tend to alter polymer's friction characteristics, as with brake pads becoming squeaky in humid weather, much like my truck's composite clutch plate and brake pads become grabby after sitting overnight in damp conditions.
Tires stored in a plastic bag here show no cracking even after 30 years I've found, as I've actually put a few 80's tires into service in the last couple of years.