I was just looking around at the local Northern Tools and Supply store. They have battery boxes, but the lids to those detach, they aren't hinged. But they also have some Utility Boxes, a bit smaller than a battery box, that have a hinged lid, with gasket. (I think these are a plastic civilian substitute for military ammo cans, hence, the gasket). They actually have a hasp for a lock, although of course it's plastic, too. As my boss once said, "It will keep an honest man out." Seems like I saw these in Walmart also, in the hunting department. There are also a variety of plastic tool boxes that might work.