Keeping the vents closed that long will insure that the seals "mold" to that vent shape. I think you will be hard pressed to keep all the air and water out with hardware weatherstripping.
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Umm, yeah, well, back to the question, yep you need to let those things sit. I suggest doing it in now and leaving them closed all winter. It's cold enough in a Series in December so you won't have the vents open very often. Just get the 3M adhesive and a friend to push in on the vent cover and you're all set.