I have had the great fortune for many 30 cal and 50 cal ammo boxes to find me over the years.
None of my surplus cartridges are loose in the can. There is packed bagged stuff, but the rest stays in the 50 rd boxes. Depending on the size of the round, you can get 6-8 boxes in each can without overstuffing it. During the last squaring away of the load out closet, I also added a homemade desiccant pack to each can.
I made them from dollar store panty hose, zip tied on both ends, containing about a 1/4 cup of silica sand. There are other versions on YouTube, but it cost very little to make these, and there is plenty more material for more packets. These packets also went into totes/ cases containing webgear, uniforms, and other tactical gear that might suffer from being locked in a closet for a long time.
While doing that project, I also managed to dehumidify the closet by hanging larger silica packs on both sides of the closet, and adding an open bucket of Rid-Ex. Six months later, the closet still smells fresh, and even the bottom of the gear tote has lost its musty smell. We have all experienced that moldy smell on our olive drab stuff, and I can say that doesn't happen in my gear room. Good luck.