I keep 2lbs of Goex in the house (garage) , the cans from which I'm filling my horns...about another pound in various horns. Someone gave me one of those repro Winchester wooden ammo boxes, and I have about 15lbs of various grades of Goex in that box, with a hasp and lock, in my yard building, about 50' from the house. I've stored powder this way for about 6-8 years with no problems from dampness.
I also store my garden tractor, and its gas supply there, and a spare 20lb propane cylinder. I have not put a warning on the building, but the box does have a warning label, as well as the word "Winchester" writ large...I figure by the time our local rural fire guys get here, the building will have burnt down or blown up...Hank