Best day bag for heat resistance

I have a 9 6 EPS board that I absolutely love. My only issue with it is that I can't fit it in my car, and keeping it on the roof, i get paranoid about it getting overheated. Ideally I would be able to keep it on the roof for 2~3 hours under the sun in OC... but I'm not sure if that's even something reasonable to hope for.

Anyways... what's the best day bag for heat resistance?