I took the old heater core out and run the water through there. I rigged up one of those big computer fans to blow air through it. I've got a picture here at the bottom.
Porsche 924 Electric Conversion: Batteries!
Being in AZ I was concerned about a fish tank pump not working at high temperatures, so I found a pump designed for solar panel cooling that's good up to 80 C. I got a friend with a CNC router to mill out all those channels. If you want to make one just like it, I have the CAD model that you could use to generate the tool path.