spent a summer in Tucson, no ac just the swamp cooler. BRUTAL. he claims 4+ hours with a gallon of ice.
Our ac unit is only a few years old and it seems to be pretty efficient. It bumps the electric bill about $20 on the hottest month. I think that fan might come close to using the same amount of electricity, since it would probably be on 24/7. It also takes electricity to make ice. The tire and resin chair I burn on earth day usually offsets any carbon footprint reduction I may experience.
That's mostly particulate emissions. You should leave your truck running while the AC is on to offset.
But it will cycle more frequently when something that's not frozen is put into it, using more electricity.
That would be great for camping in a tent. Get a deep cycle marine battery and a small solar panel. A tent in the middle of summer can be "sticky" in our humid climate.
That it's an awesome idea. I've sat in the trout stream a few times when it got HOT while camping in eastern Oregon.