If its your good board you might not want to leave it in the car for more then a few times. I would crack the windows and maybe find some shade to park under. Maybe wet a towel or sheet to keep the wax from melting. Other then that you should be ok.
Was always wondering.. to what extent does a bag help? can I leave my board in my 110 degree car in a bag for a few hours with no worries?
heat reflective bag + windows cracked = no worries. most of my surfing is done before or after work, so i leave my board in my truck regularly & have never had a problem. i didn't even start using "day bag" type bags until recently...all through my teens & early adult life, i just used a sock. if i think of it, i try to park where it'll be reasonably shady through the majority of the day, too. but that doesn't always happen.