Hmmm ... It does appear that I am a bit confused. I am currently doing a swamp cooler in an actual cooler with some frozen water bottles tossed in. For some (drunken) reason I thought that adding a lid would make it better. I guess if I want to go with a true swamp cooler I would need to focus on maximizing the evaporative cooling properties. If I want to chill my carboy in a cooled tub of water I would need to focus on maximizing the insulation properties of my tub. Given how well my current hybrid system of swamp cooler, fan, and chilled water is working, I may just stay with what I got. It is holding a steady 68 degrees in one of the hottest, most humid, prolonged heat waves that I can ever remember. All I have to do is swap out the frozen water bottles each morning and evening so it is a pretty simple system to maintain. Problem solved, thanks!