Personally, I would look at who's already solved this problem and then if it ain't broke, don't fix it.
Shrink wrapping, vac-packing, etc all might seem like a good idea in theory, but has anybody actually tested this over a long-haul duration to find out about real world issues?
The US military has been storing ammo the same way for almost 100 years. In ammo cans, in bulk, not plastic wrapped, etc. Just kept in a warehouse in controlled conditions.
Not sure how many guys remember this, but WW1 and WW2 surplus ammo was routinely showing up on the sporting market well into the 1970s. While some of this ammo didn't look pretty, it was very reliable given that a lot of it was 50+ years old.
I know there were guys down in New Zealand who were fighting those 1960s and 70s rabbit plagues by pulling bullets out of WW1 and WW2 surplus ammo and then recycling the powder and the brass because ammo was in such short supply down there during these years. Setting aside the wisdom of re-using un-known powder, my understanding is there were no significant issues with the age of the ammo.
Bottom line is that brass case ammo, kept in reasonably controlled conditions, the lifespan is already very long. I'd be wary of introducing more problems.
Grouse