Wish that would work down here in swampland!
But I'm diggin your idea, here are a couple of links that I found how some guys solved his need for a diy swamp cooler!!!
RAT-LOOK.COM • View topic - How to make a swamp cooler for a fiver !
DIY Inexpensive Swamp cooler air-conditioner for your car or camping - YouTube
Good luck and show us the photos of your final product!