I had two revolvers in my '97 Ford Ranger at the time I lost the truck to an engine fire. The Ruger Security Six (38+p ammo) was in a portable safe under the seat, the other (an NAA mini-revolver in .22LR) was in the glove box. It was hot enough in the cab to melt the ceiling lining, the rear view mirror, the GPS bracket, the rifle rack on the back window, half the dash-board around the glove box and anything else made of plastic or polymers above seat level. Everything on the floor of the cab, while not melted, was covered with puddles of everything that DID melt, as well as the glass from the windshield when it shattered from the heat.
Once the fire was out, the firemen carefully handed me both still-warm-to-the-touch and now dripping wet revolvers. The ammo in each was still intact with no cook-offs.
I think that was just a wee bit hotter than your typical left-in-the-sun-in-summer car temps.
