Given where you are and if your trailer is largely stationary, a swamp cooler may actually make some sense. It humidies as it cools and humidity is normally a rare commidity in the cooling season in the Mojave. The only exception would be the monsoon weather we have been going thru over the past 3 weeks.
My only reservation would be the water quality where you are. Look around the stick houses near you and see how many swamp coolers are being used.