I'm thinking that even in a "cooler" (which won't prevent interior temperatures from rising, but only slow down the "rate of the rise"), platter-based hard drives may end up having problems -- due to the fact that they have moving parts and lubrication inside.
What I do:
I keep my most important backups on USB flashdrives, which I then place in a ziploc bag along with a desiccant to (hopefully) reduce humidity.
Then, I keep the bag inside the car interior (storage compartment in center console).
I've been doing this for around a year now, through the heat of summer and cold of winter, and the drives seem to be doing fine.
I'm thinking that the same strategy might work with a 2.5" form factor SSD as well.
The downside:
Limited storage space, unless you're willing to maintain a "flock of flash drives".
But again, my intent is to protect only the most-important data from "home disasters".
The rest of it -- well, it's expendable...