While I generally agree with most of your post, I'm not so sure about this part of it. Maybe because I am unclear of the message you are trying to convey???I'm not so impressed with the idea of keeping ammo in a hot car for the long term.
Ammo is stable in a hot trunk. The military ships it in cargo containers that sit out in the sun for long periods of time. Heck you can buy 20+ year old surplus ammo that has been stored in varying temperatures. I even know a gun dealer who stuck several boxes of factory and several boxes of handloads in a trunk of an old Ford in the desert (New Mexico, near Farmington) for 3 years to see what would happen. He maintained some ammo from the same lots in his home for comparison. He took a few rounds out every six months or so and tested them to see if the performance degraded. It did not not, at least not that could be determined in a 3 year period.
Now if you are saying it is dumb to have a bunch of ammo in the car because people will steal it, that I will generally agree with.
I tend to have an extra couple of loaded handgun magazines in my car, of various types/calibers for the various guns I carry. But none are kept visible.