I believe any tight-fitting car cover used outdoors, regardless of quality, promotes corrosion. It traps moisture, is vulnerable to wearing of the finish from wind motion and is an invitation to rodents.

If you store outdoors, I believe getting it under a roof of some sort is essential even if it is only a canopy. They can be surprisingly reasonable in cost and can be either fabric or hardtop.

When I lived in Noank, CT I winter-stored my Harley-Davidson by building a lean-to frame against the house and covering it with a plastic tarp. It allowed air to circulate while keeping the snow at bay.