I have tried three different bike covers. The first one was from http://www.bicyclecovers.ca/ This one is adequate at best. Would last maybe a year out in the elements. If I didn't have to pay shipping and taxes, it might have been somewhat worth it, but I would never buy one again. The other two I bought in Japan. One was garbage and fell apart the first time I used it. The other one was less than twenty dollars and is fantastic. It is durable and has draw string to tighten against both of the wheels, with velcro in the middle.

Now I know this really doesn't help you exactly but my point is try to buy one of the better ones if you are going to be using it a lot.