How do you cool you motor in between passes?
If you have a boxfan that means you have access to power. I ran a setup in the duster that worked extremely well. The motor would be cool in around 10mins. I took a decent sized cooler (any bucket would do), added a sump pump, filled with water, with 2 hoses that were attached to the heater hoses on the motor using 3/8" air line fittings (mine had to be hidden so i ran the factory heater hoses down to the floor board under the dash) Between rounds hook up the lines, turn the pump on, and let it circulate.