I'm installing the glare shield and have thought about the possibility of some vent holes along its forward edge to allow the heater fans to circulate some warm air by the wind shield during winter operation. The way my twin heater fans are wired they currently push air down through the heater core and into the cabin under the instrument panel. Can the polarity of these fans be switched to cause them to reverse direction? If so I could conceivably have a special switch to reverse the polarity to push air up to some vent holes in the glare shield when needed. I've scoured the forum for pictures and have seen a few glare shields with holes but most don't have any so I'm wondering if the holes work to keep the windshield from fogging up or if fogging simply isn't it an issue. Does normal airflow through the cabin with the heater running keep the windshield clear without any vent holes? The winters get cold here in Northern Illinois.