Don't think you'll have any issues at all, but then no one wants to get burned sliding a hot gun into a close-fitting concealed holster either. So let's consider the sources of heat so that we can find cooler storage areas...
Radiant Heat. In this case, all radiant heat comes from the sun. So any storage place out of the direct rays of the sun will eliminate this possibility.
Conducted Heat. The gun would need to be in direct contact with a hot surface, such as the top of the dash, console, or seat. I seriously anyone is going to leave a gun unattended in those places, so this is not really realistic.
Convection Heating. A locked and sealed car can get very hot in the summertime, but the still air quickly stratifies into thermal layers. The hottest of these is near the roof; the coolest near the floor. While the upper middle interior could easily go to 50?F higher than ambient, the floor could easily be 10-20? cooler.
If you have a sun roof that pops up leaving a small gap, a truck with a sliding window, or opening the rear side windows even 1/4 inch, then the air inside begins to circulate and vent. In this case the temperatures will not be able to build much above ambient.