Funny you say that. This is the one I haveI use a tool/utility cabinet mounted on the wall. Keeps it high up away from stuff, and you can put several tens of thousands of rounds of various types in there, in ammo cans, MTM boxes, factory ammo, etc. This is also how I store magazines, in a separate cabinet.
Like this: https://www.lowes.com/pd/CRAFTSMAN-...yWvQRzob7vajs9t6708aAmIiEALw_wcB&gclsrc=aw.ds
Steel Freestanding Garage Cabinet in Red (32-in W x 74-in H x 18-in D) https://www.lowes.com/pd/CRAFTSMAN-...-Steel-Freestanding-Garage-Cabinet/1000476967
It uses a key. I could bolt it down to the shed. Throw desiccant in there and check it periodically? It’s great for ammo and accesorries. Thoughts?