Hi EddieZ - this is good info. Do you have to pop any of the interior caps off (ie. near the rear door of the driver side) to get max airflow? Is the airflow created by removing the plastic cap(s) noticeable? Are your interior walls covered? If so, does it hinder the airflow from the D pillar vent opening?You may have an easy solution to the rear air intake need. Under the van, at the bottom of the D pillar on both sides, there is a 3x4-or-5 inch plastic plug that can be removed. I've been running without the one on the driver side (passenger side is too close to the exhaust) for about a month. Need to devise some rodent screen for it. In a cargo van, there are plenty of holes and openings on the D pillar, for the air to come through.
Beside that, the cabin air exit vents (which we assume have one-way flaps), are hidden under the black side moldings behind the rear wheels. It has been speculated that these could be modified for air intake, but, no one has yet taken a shot at it.
I need to figure out how the air flows from the opening of the D pillar and into the cab I suppose. Perhaps you can shed some light. Thanks!!!