I do not reccomed that West Marine cover as a winter cover. Especially when they are fastened under the ttop instead of over it.
I have a fisher cover, it is the best cover I have ever owned, it breathes, has pockets for 2x4 supports on the outside of it and it keeps rain and SNOW out(yes they are expensive but it is worth every penny). Most people will get around 10 years out of them (no I cant say that just yet).
The problem with the west marine style is that the first snow storm will collapse the cover and stretch it.
Just my experience. Take it for what its worth.