As far as my "fridge bizness" doesn't include climatized car, I can't help you...
... if you need to drink, I suggest you water. But if you stop in a quite large city (such as Le Mans), just have a look as wine sellers, such as Nicolas stores or even independant shops. They all have wine and champagne to sell welll chilled.
Maybe you can include on your roadbook some wine cellars visits, because cellars are always well tempered...
... and if you stop at Le Mans, maybe we can have a drink together.