The worst thing you can do is take powder/primers, as components, from an airconditioned house, outside to an un-airconditioned environment for reloading. The cool containers will condense slightly regardless of your best efforts, and you will be adding moisture to the components every time you do it. (On a winter hunt, ever bring a cold, scoped rifle in from the cold, and try to look thru the scope?)
It's better to keep powder and primers in an un-airconditioned garage, even tho' it's hot, .... as long as they are in original containers and sealed.....than it is to take them back and forth repeatedly from cold to warm to cold etc etc. (The ammo found in The Lady Be Good B-24 bomber was found to be perfectly useable even after almost 20 years in the Libyan desert at 120F days and 40F nights, chiefly because it as already assembled ammo...not components. Heat did not deteriorate it.)
I have personally fired 12 ga shotgun ammo that lived in a Texas car trunk for 12 years and it chronographed exactly as it was originally advertised.
Doesn't prove anything, just anecdotal interest.