That would only work in the lower humidity locations, and at that, not produce that much cool, especially when you are parked. IMO, get a Koolatron (brand name) solod state refrigrator if mobile refrigeration.

I believe this idea is implmented in a crude form in most automobiles under the name of "Radiator" to cool the engine.

I think you can track this idea back at least to the horse cavalery. They wet the cavass on metal canteens to keep the water cool on a ride. I have seen similar devices sold in Arizona to hang out of a car window. One word of caution: Don't assume that it will keep foods cool enough to prevent food poisoning.

A cheap styrofoam chest, half-filled with ice, works better. If you don't open the lid it can keep food safely cold for several hours. A bag of ice is still relatively cheap, and you can find it at just about any store located close to an Interstate.

Koolatron coolers work fine, if the cabin temp is 70 F or lower- they cool things 25 degrees lower than ambient temp; that's why they're called "coolers," not "refrigerators." They may also be used to heat food to about 120 F, great for canned foods or food that's sealed in a sterile pouch.

Also, the energy used to cool using the evaporative method is going to be produced by the car's engine- "ain't no sich thang as a free lunch..."