A couple of guys here in town that used to do "remanufacturing" of ammo had two of those. Fortunately, they never had to serve their purpose (other than to securely store the powder), but they did satisfy the law regarding powder storage.
As far as insurance goes, I've talked to my agent and he said pointed out the section in my policy that says something along the lines of as long as the amount of ammunition, gunpowder and related supplies isn't in violation of the law, it's allowed. Of course, your policy may vary.
I'd also be more concerned with the LP gas bottles in my garage. And maybe the can of gas for the lawn mower. Still, if it gives you peace of mind, it's probably worth the money.
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