As hot as it gets in car in AZ, (just got back from 5 days, 20 miles West of Gila Bend) it does not get hot enuff to pop a primer. Takes over 300 degrees.
If you think it is hot where you are, you can chat with some of our members currently in Iraq. They also have some loaded ammo along with them- usually in the ammo can hanging on the mount of the .50 Browning.
Now, realistically, it may shorten the lifespan of the ammo from 60 years to 15 years- cool and dry is best- but in the short term, it don't really matter. It DOES increase pressure/velocity when it fires, but unless you are shooting long range rifle, doubt that you would even notice.