Complete Swamp Cooler - How to build a low-cost 12 volt evaporative cooler. My husband and I built two swamp coolers that we use to air condition our tent when we camp in hot, dry weather at Burning Man.
Just two clay pots and wet sand. Award winning Methods of Alternative Refrigeration--awesome site with TONS of great ideas on every preparedness topic imaginable. And the emphasis is on doing it as inexpensively as possible.