Thanks for the feedback. It's our spares that we want to keep chilled just in case our primary supply fails.
How long are you away for, and how much do you get through?
Personally, and I don't like waste, I'd be inclined to take the spares in a Frio and then if it goes beyond the 30 days unopened, I'd jettison those vial/pens/whatever, provided it wasn't too much.
I doubt you will find a car fridge assuring a specific temperature as the usually cool to a set figure below the ambient temperature, to a maximum reduction to around freezing point. So, if the temperature is 25c and the fridge states it'll cool to a reduction of 20c, the fridge would end up around 5c.
Would you be truly willing to be confident in that? If I recall our last vehicle fridge was a couple of hundred pounds.
If you take a spare (unfilled) prescription with you, you would likely always have a safety net anyway.