I only need the cooler to get me through hot areas and when I stop it's someplace with ice to rechill the interior.

Compugeek gave me a great idea with the indoor/outdoor thermometer though and for that I thank him. I ordered one of the wireless units and will instrument the back/storage area of the truck and may put a second sensor inside the cooler. First I get to experiment with temp differentials over time, but after that it can be used to monitor storage temps driving across the desert on trips. If cooler temps get too high it's time for more ice.

Unlike Compugeek's car, I don't have that big piece of glass acting like a greenhouse over the bed of my truck -- never liked hatchbacks and SUV's are definitely no better. To play on Desperado's solar panel idea -- maybe a larger flat panel could be used to block the light coming through those big pieces of glass and provide power to a cooler -- that might be a great idea.

I have a white pick-up with a white fiberglass bed-cover which should do a fair job of keeping the storage area to a max of ambient -- or so the theory goes. The black asphalt road may interfere, but to what extent? Now I can find out.