You're dead on about the temps. Lows were overnight, and the car was also in a garage, so its surroundings didn't even go that low. (I don't have a thermometer to use for the garage, though )

I thought about opening the trunk and cooler at night, but that's more work than I'm willing to do. (You got to know yer limitations.) I'm exploring other options to see what their effects are.

This week, I started with all four bottles frozen solid.