All about 'Swamp Coolers' aka 'Evaporative Coolers'
Swamp coolers use water evaporation to provide cooling that is then blown by fan throughout the trailer. They are only effective in hot dry weather. Certainly a reasonable cooling alternative for the desert areas.
"After a bit of searching and asking around we learned about that strange thing on the roof of our old trailer. The Swamp Cooler.
The best explanation I have heard to describe the concept is to imagine putting on a wet t-shirt on a hot day and then blowing yourself with a fan. The rapid evaporation of the moisture provides considerable cooling effects."
Swamp coolers became quite out of fashion and almost suggest 'old'. But there may now be some resurgence. They can be more economical to operate than air conditioners and will save on energy. They require some regular maintenance but do seem to be quite an affordable means to provide some relief from the heat in earlier fall and later spring.
The following websites provide good information on both the value and use of a swamp cooler and how to maintain and repair them.
Buying and Using a Swamp Cooler ... article plus other referenced items on swamp coolers and saving on cooling ... from associatedcontent.com.