I have used one of these: Amazon.com: Koolatron Slim Compact P20 Thermoelectric Iceless 12V Cooler Warmer, 17L / 18 Quart Capacity, For Camping, Travel, Truck, SUV, Car, Boat, RV, Trailer, Tailgating, Made in North America: Automotive for ~10 years and it has been great when I have pre cooled...