In areas with low humidity, regular air conditioners don't work very well. A simpler solution uses water evaporation to cool and humidify air. These are called evaporative coolers or swamp coolers and are used in homes all over the Southwest U.S. Air is pulled by a fan across a wet pad, which lowers the air temperature by 20-30 degrees, and provides much needed humidity as well.
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.
A Practical Zeer Pot (evaporative Cooler / Non-electrical Refrigerator)
The Lifesmart indoor/outdoor coolers are almost perfect for camping. It is an evaporative cooler so your tent does not need to be insulated to keep cool, but rather have open ports to keep cool air flowing. A gallon of water delivers up to 10 hours of run time for the unit and it uses less energy than a 40w light bulb. The 350CFM airflow will keep an area of up to 250sq m cool. Its stands 21 inches tall and weighs 10 pounds and has an inbuilt carry handle.