
I found this rather simple design on youtube.com for an Evaporative cooler or swamp cooler.
I used a drywall compound container for my evaporator with 2 inch holes drilled all around the top of it. The container was lined with cotton insulation found on external dish washers then held in place with chicken wire.
To circulate the water I used a small 12 volt self priming pump and a piece of PEX with small holes drilled along the length of the tube then one end was heated to the melting point and crimped shut.
A hole was cut in the lid of the container to the size of a 12 volt computer fan and fastened to the lid, the thermal switch the fan uses was bypassed with a variable resistor so I could vary the speed of the fan. A PWM was also added to the pump to control the water flow.
Cheers Hitman