If your thinking about fire,,
Then build a box using 2x wood,,2x4-2x6-2x8-etc,,
keep the joints tight and have a lid that's 2x also.
Here's the gig,, fire needs oxygen to burn, a tight box doesn't allow oxygen and/or fire to consume the entire thing, the outside will char and the lack of air moving through said box will keep flame from the interior. Unless a house is fully engulfed and destroyed,, using the burnt side of standing/remaining structural lumber is how they find the "source" while investigating cause,, much of a house fires structural lumber remains un-burnt.
I talked to our local Fire Chief about powder storage and what they do as firemen,, his answer was they don't worry about it,, powder in jugs doesn't "explode",, it burns off in a "poof".
The fact is if BP is exposed to high heat without an ignition source the sulfur component changes and powder looses much of it's "explosive" properties.
During that conversation with the Fire Chief I mentioned I'm using GI ammo cans, he smiled and said "Well you can't beat old reliable"