The trunk flow-through air vents (black plastic grill about 3" x 4" under the fenders) allow reverse air flow into the passenger compartment from the trunk when negative pressure exists in the compartment, such as when the sunroof is open. Besides the trunk/spare tire smell, under some conditions of speed and wind one can get exhaust sucked in through the left vent--very unpleasant and potentially dangerous.

Is there some modification or improved part available that only allows air to flow out through these vents and not inward? I was thinking of adding a rubber flap to these vent grills to allow air to flow only outwards. Has anyone tried this?

Thanks