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.
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...
I would use an onsite local backup and a cloud service like Google Drive, Dropbox, or OneDrive before resorting to using the trunk of my vehicle as a backup plan.
I want a second place to keep my hard drives that is not my apartment. I'm going to use my car trunk. Any advice? I live in NYC and it gets hot in the summer. Should I put them in a lunch cooler?