My company is looking at these units to put on our trucks. Basically, while you're driving, the unit freezes a huge block of ice. When you shut down, it blows air across the ice, providing cool air to the cab. The info says it only draws 6-10amps while in operation.
http://www.webasto.us/am/en/am_trucks_aircon.html
Looks pretty cool. I was listening to Landline Now last night and they were talking with someone from Kenworth. I guess you can get a similar system like this from them when you buy a new truck.
Couple that with a diesel fired heater (like the Webasto we already have) and you can go without an APU or idling.