If you don't mind, could you run some tests with the unit plugged into the car? The sled looks like it will severely restrict your air flow. I'm curious what the delta will be for temperature reduction. Of course if you wanted to be really thorough, you'd have to test with and without the fan. :)

You could always avoid doing mods to the empeg and make mods to the sled instead by attaching the fan externally. Of course this way the fan is permanently installed in your car and you can't make use of it when playing the unit at home.