Re: medium and long term storage of ammo
Different approach, use a "food saver" vac to seal ammo in plastic bags and then store in whatever carton you want. Commercial ammo can be bought in similar packaging. I have been impressed with my foodsaver as it keeps stuff sealed and fresh, no freezer burnt fish or deer; I have used it for ammo and parts.
After Katrina some of the groceries that I released into the floodwater (in foodsaver bags) had rotted in the sun for a month, nasty, but even though the bags were swollen like footballs they did not leak a drop or smell. If this system can do that it will keep your ammo fresh and dry.