My experience with powder storage
I worked for 20 some years in engineering for an aerospace ordnance company that specialized in pyrotechnic devices for military aircraft and space vehicles. Some of these devices used common reloading powders such as Bullseye or Unique as gas generants for piston driven, single use devices, for instance; pin pullers and latch operators in escape or ordnance arming systems. Black powder, used for igniters, was stored alongside the smokeless.
Commonly these devices had a 5 year operational (on aircraft) or 10 year shelf life after which these would be returned to us for refurbishment or disposal. Upon return, we would perform “lot verification” tests on approximately 10% by firing these at the extremes of their operational environment (normally -60f to +140f IIRC) and this data compared to the data collected when the devices were originally qualified. Then, to refurbish the remainder, the original lot of propellant was used if possible as a replacement. Using the original propellant lot allowed us to use a smaller acceptance test group and abbreviated test regimen-PROVIDED: no statistically significant difference in performance was exhibited in any of our test samples; original, return or refurbished.
I know of no case where we witnessed a change in performance due to propellant degradation. When deployed, these devices (and aircraft) were subject to conditions that ranged from the Sandbox to Siberia. Our replacement propellant was stored in un-insulated steel magazines about the size of a conex box or semi trailer, painted dark red. These were placed on the back of the company property here on the Colorado prairie. Not an extreme environment but -10o f to -20o f in the winter and 90of to 100of in the summer. In the summer these magazines were stifling inside. The propellants and black powder that cycled through these extremes for 10-20 years suffered no measured ill effect.
Lastly, anyone storing propellants inside their house might want to check their local fire codes. If you are improperly storing flammables and a firefighter is thereby injured, you will be held responsible AND your insurance company will laugh at your claim.