If you are only going to be in ghastly dry places like NM desserts, you can get by with a swamp cooler built for RVs. THEY ONLY WORK IN AREAS WITH LOW HUMIDITY. So if it rains in your low humidity area, you're screwed. Do internet searches for "RV Swamp Cooler" or "RV Evaporative Cooler". If you do searches for "DIY Swamp Cooler" you will find lots of pages on building your own set up like the last link.
this is a $40 ice chest set up similar to the ones you build yourself. If you have the room and only need it occasionally, this may be what you want.
If you had said WHERE you were, it would have been easier to give you area specific info. Basically a swamp cooler will not work anywhere except desert areas.