First of all , cool and dry are the best storage conditions for powder and primers.
Heat accelerates the decomposition of powders. Keep powders cool and dry and they should last a minimum of 20 years for double based, 45 years for single based. Powder tests are run at 65 C, if the powder fumes at the end of 30 days it is checked for stabilizer content. If the stabilizer content is low, the powder is scrapped. That little factoid is to let you know that heat is bad for powder.
You want to store powders in containers that will burst easy if the powder catches on fire, self ignites, whatever. Store it in a safe, or some thick walled thing, if the powder goes the container will amplify the pressures and when it finally bursts, ka boom!
It is good practice to keep powders in their original containers, for bursting and material compatibility issues.
Primers should always be kept in their original containers. Greatly reduces the chance of them all going off at the same time.
