I live in Southern California and fly all year long and through the summer.
It is warm on the ground, especially if you are held by ATC for clearance in
Las Vegas!  I sat there one time at 120 degrees and it was VERY warm.
However, once in the air, the climb on the IVP gets you to altitude very
quickly, and it has never been a concern.  BTW, at altitude, my wife
actually has a lap blanket for her legs when sitting in the back seat.  The
front seat is in direct sun, so is warmer by at least 10 degrees. My .02

Pat Brunner
IVP - 8 years flying
700 hours