I should probably open the ammo can a few times a year whether I use it or not. Maybe burp it like Tupperware once each season when the temperature changes.
I thought I didn't have any .30 caliber ammo cans, then I remembered the one in the car with my tow chain in it. It just barely fits in there, and I lave to lay it back and forth when I put it in. Some of the jeeps we had in the army had 20mm ammo cans between the front seats like a center console. Those things are huge and have diagonal reinforcing ribs on the sides. I had .50 cal. cans U-bolted to the rear racks of several of my ATVs, with a hasp welded on and the hole in the latch enlarged for it, so I could slap a padlock on. The nuts on the U-bolts were inside the can, usually with a metal plate instead of washers, and covered with black RTV silicone. Ammo cans aren't just for ammo.
When I was in Germany and we went to the field for tank gunnery support, I took a wooden ammo crate like one of these full of pogey bait. (US, military, slang: Snacks, candy, and similar food items that are not generally available to soldiers in the field.) Pogue is American pejorative military slang for non-infantry MOS (military occupational specialty) staff, and other rear-echelon or support units. Also spelled POG - for People Other than Grunts. Sometimes we were called REMFs - Rear Echelon Mother F***ers, usually by DATs, Dumb Ass Tankers. I didn't care what anyone called me, as long as they didn't call me late for dinner. But if they did, I could fit a lot of ramen, jerky, chips, and other stuff in my ammo crate.
I know I mentioned it before, but our mess sergeant gave us loaves of bread and cases of shelf-stable UHT milk. IIRC it was 24 200ml cartons with straws attached like juice boxes, but before I eer heard of juice boxes. The milk didn't need to be refrigerated, but if you kept it in a fridge it would last 10 years. In the winter we threw a case on top of one of the trucks and took a carton out to thaw whenever we wanted. If I wanted toast, I tossed a slice of bread on top of the tent stove. There's nothing like that good old diesel flavor to give a man an appetite.
The bread, milk, and pogey bait supplemented the C-rations and army chow we had every day and made life more bearable. The treated wooden crates were poisonous but no one cared. We didn't eat the wood.