Here are some tips for you:

Military cartridges are designed to be stored at temperatures ranging from minus 65 degrees Fahrenheit to 122 degrees Fahrenheit.
Military cartridges were created for soldiers to use under the worst conditions imaginable. These same cartridges also have an indefinite shelf life. The term shelf life refers to how long an item can remain in storage and still be functional.

The companies that manufacture military ammo are well aware of their requirements and specifications.
They are also well aware that if they do not meet the criteria, they will lose a rather large contract with the US Government. The interesting thing to note is that the same companies that create and sell ammunition to the government are the same folks that make most of the gun ammo we civilians use. The same people that create the 5.56mm for the military change the label, call it a 223, and sell it to civilians! When it comes right down to it, there is little to no difference in the ammunition common to civilians and military. Therefore, it is generally safe to use similar procedures in storage methods and practices.

Most ammo comes in a wooden outer container with metal inner packs that actually hold the ammo.
The military stores ammo at least two inches off the ground and they make sure that it is inspected every five years. Standard procedure is to actually look at just ten percent of all the ammunition to see if any defects have developed. Once the ammo has been inspected it is placed back in storage for another five years. If any corrosion has developed on the ammo, copper or steel wool is used to scrub and scrape it off.

The number one adversary of ammunition is moisture.
As long as your container is waterproof, you should not expect any problems. Another common military tactic is to include dehumidifier packages in the ammo containers to suck up any surplus moisture that may have gathered.