My reloading set up is in my garage.I store my powder above the reloading bench.My garage is climatically controlled (A/C and heat).Never had a problem with the heat and cold variations here in Texas.The worse thing you can do is store powders in an enclosed metal storage container.Basically a grenade waiting to explode.Years ago while living in California, I went into a Big Five sporting goods store, and they kept the powders locked up in a huge gun safe in an isle with the reloading equipment. I asked the manager why, and he said due to theft.I told him about the potential hazards and sure enough,two weeks later it was removed and placed on high shelves behind the counter.Never,ever store your powders in a tightly enclosed metal "box". Wood is preferred,as to vent in case of fire.Powders are not explosives,they are flammables.