BigBore45, I count more than 20 lbs of powder. ATF rules require that an individual that has more than 20 lbs of powder store it in a wood box made of at least 1" thick sides.
I just completed making boxes for my powder. They are actually several small boxes with 1/2" sides that fit in a big box that has 3/4" sides.
From what I have read, the idea is to have at least 1" that a fire would burn through before the powder would burn.
Do not put powder in a sealed container because if the powder goes off in a sealed container, it could possibility cause an explosion when the gases caused by burning powder create a pressure that would cause the sealed container to blow.