I have an indoor/outdoor thermometer to keep track of how hot the back of my Expedition gets. I drive pretty regularly with two dogs in the back, and over the summer and winter the temps can get a little extreme.
I need to be able to take it out to keep an eye on it remotely (it has about 1/4 mile range) but also have it not rolling around while I drive.
There was a coin holder there that I popped out, and used as a template for an insert to keep this mounted semi-permanently.
Printed with kinda crappy Amazon Basics PETG. If it holds up well, I'll reprint it with better quality black PETG so it matches the car better.
We've had a couple 100 degree F days, and the thermometer read 110° a couple times, and the plastic seems to be fine (so far).
It's mostly out of the sun, since it's low on the dashboard, so I expect it'll hold up.
Mine is sadly right in the window, but I might get tint at some point so that should help.
I see you have a window shade, but do you also have tint? On 100f days my interior gets well over 110 even with my shade up.