I just couldn't leave well enough alone and installed a 5.2" Spal paddle blade pusher fan to force approximately 300 CFM through the pop-up vent no matter what speed I'm travelling at. This little fan is not subtle about the movement of air as you definitely know when it has been switched on by the satisfying sound it makes.
This installation entailed fabricating an enclosure from 26 ga galvinized sheet steel that completely seals the underside of the pop-up vent and provides a base to mount the fan.
The two sides and flanged mounting surfaces were all fastened with 3M VHB tape. So far after a week of driving around all of the seams are holding strong with no signs of the pieces separating.
Like the pop up vent I coated the finished enclosure with Rustoleum rattle can truck bed liner, attached the completed assembly to the underside of the hood using 3M VHB tape, and sealed the perimeter and all interior/exterior seams with black RTV silicone to form an air and water tight seal. The RTV silicone provides some adhesion between the enclosure and the underside of the hood but the majority of the "sticking force" between the enclosure and hood is provided by the VHB tape.
I will need to drill a couple of small drain holes in the enclosure to drain any water that may enter the vent.
Now I just need winter to be over so I can put this fan to work during the summer when it's needed.
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