I made an air conditioner for my car a few years ago. here is a similar idea with pictures
http://www.instructables.com/id/Homemad ... nditioner/mine used an automotive heater core ($20 on ebay), and computer cooling fans ($5 each on ebay for the size I wanted)
I used a 30 can plastic cooler for durability, I found the marine coolers had better handles and were not as bulky, and being white wouldn't get hot from the sun as quickly. I used a live bait well pump ($30 at wallyworld) I filled a bunch of 1 qt juice bottles 3/4 of the way and added as much salt to the water as they would hold. I made the lid with the plumbing seperate from the bottom to be easy to transport for filling.
it all worked ok. however it couldn't cool the whole car thanks to untinted windows and the solar heat coming in. In an insulated TD it would work, one guy on here has already tried it and said it kept his TD at 70 for 6 hrs. Make sure the heater core has a drip pan underneath it that drains into the cooler as the condensation it removes from the air will create quite the puddle. use this to cool your intake air and set up a thermostat to turn the pump off and on to maintain temp. I plan on adding this to my TD someday using two computer fans, one to draw in outside air, and one to recirculate cooled TD air, running on 12V the fans draw very little, and the bait well pump also draws little.