Safest place is on your wrist.
When you forgot to charge your Apple Watch before going out...I don't really see a reason to take the watch off while driving. Just seems like a waste of time imo.
I have had the watch for 3 years now, that use case has never once come up for me. Seems like it would make more sense to just have an extra charger in the car with one of those portable USB chargers. No need to add a permanent "charging station" for it unless you plan on doing it everytime you drive. If for some reason that is the case I would suggest the one linked below. It has adhesive on the bottom so it stays in place.When you forgot to charge your Apple Watch before going out...
That's never happened to me in three years of owning a Watch or two.When you forgot to charge your Apple Watch before going out...