I've got a handfull of those tall ammo cans (for mortar rounds). I think they are about waist tall and about 14" by 6". Big enough such that if a guy was to load one up, it would/could be too heavy to move around, but would work for burying I suppose. I've got a bunch of them loaded with 8mm, and can't hardly drag them around on the floor!
A few years ago I was swimming in ammo cans. That has pretty well dried up and these are the remnants.
I read on some other website the ticket is to fill the can with whatever, drop it in a heavy-duty leaf/lawn plastic bag and seal the open end with hot glue, then bury it. The bag pretty well stops whatever moisture in the ground from attacking the can (they rated the can at 20-30 years by itself). The article did mention digging a little deeper than you want the can, and putting a few inches of gravel/sand to allow the moisture to drain below the unit.
