Did the black car, white car in the sun test, I think the top temp in the SanFrancisco sun was 126 degrees both cars & the black car got there first... I don't think a gun in a glove box (or ammo) would get hot enough to either damage the gun or set off the ammo
I wouldn't reccommend leaving you Glock on the dashboard tho, I might add
A windscreen sun reflector shade thingie might be adviseable, in any case, will stop you burning your butt (among other things) when you get in, too