Yip,
Ammo cans.... perfect. That's what they were made for - small arms ammo, hand grenades, mortar shells, rockets, flares, etc., etc. Get the big 20mm cans if you have a lot of powder to store. And roundball is correct - by Fed rules, you can store up to 50 pounds without any bureaucratic hoop jumping. As far as the locals go, it is always easier to get forgiveness than permission......translation....don't ask, don't tell !