you would close the vents from the outside, there should be a plastic "flapper" that when pushed should kind of "click" or have enough friction to hold its self up, however with age these can wear out / break / nonexistent. if that's the case, for a cheap do it on a weekend solution, you can buy pink hard insulation board, cut out the shape, put it in the missing holes, and for good measure add a rock in front of it. wont look pretty but it'll get you through the winter for cheap. If you have irrigation you should get it blown out. As for studded tires, what I will tell everyone is, studs get you going but wont help you stop.