I've had the less-than-wonderful experience of summers in Oklahoma, Texas, and now Louisiana going back to the mid 1970s. In all of them I've regularly had a spare mag or a box of ammo kept in the vehicle. I use the 6-month rotation mentioned and have never had any trouble.
"PLAN FOR YOUR TRAINING TO BE A REFLECTION OF REAL LIFE INSTEAD OF HOPING THAT REAL LIFE WILL BE A REFLECTION OF YOUR TRAINING!"
doubled
"PLAN FOR YOUR TRAINING TO BE A REFLECTION OF REAL LIFE INSTEAD OF HOPING THAT REAL LIFE WILL BE A REFLECTION OF YOUR TRAINING!"