When my folks moved out of their house in Boise, my dad found about half a pound of black powder in a pipe tobacco can in his shop. He remembered that his dad had that can of powder in his shop.
It made it through at least 60 years of high desert searing heat and bitter cold (maybe more...it might have been my great-grandfather's) - and still worked just fine. Neither shop ever burned down, either. In fact, if it belonged to my great-grandfather, it probably went through the US Mail when he mailed all of his guns in a big old crate from Jamestown, ND to Caldwell, ID just after World War II.
I absolutely do not recommend a pipe tobacco can in an uninsulated shop full of metal- and woodworking tools...it's just an anecdote. My powder is on the top shelf of the closet in a back bedroom where I do my reloading. It's away from prying eyes and out of reach of the occasional miniature person.
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae