(Update from 4-22-08: I'd forgotten that I mentioned the gas heater on here. Last fall the gas tank and heater were removed, and a ceramic heater was built in. It works great, although not quite as fast, and doesn't use gas.)
However, air conditioning is trickier because the shaft of an electric motor doesn't always spin. Some have used a compressor driven by the motor shaft anyway, while others have turned a compressor using a separate motor. Finally, my dad came up with part of the concept for this system. It pumps ice water through an evaporator core, which has fans that blow air through it. It is very simple, but we found what we were looking for at Sporty's Pilot Shop. They sell air conditioners built into ice chests for prices ranging from $475 for a basic model to $625 for a 24V, dual fan model.There is also an ArcticAir unit for $4750 with a full compressor unit. However, we like our $10 version better. I saw the ArcticAir display at EAA AirVenture Oshkosh this summer, and our unit is more compact and puts out cooler air. All you need is materials, basic construction/assembly and wiring skills, and a bag of ice. Let's go!
Update, 5-12-08: 100,003 views! Yay! I'm no Kipkay, but I'm still proud.