My car lives outside all the time. I have 4 covers in all. A heavyweight lined one for snow or high winds, two lightweight cheap Halfords small nylon ones and a custom John taylor storm cover that covers the rear mohair wheel cover.
The Halfords covers are very light weight and blow about a lot but tend to allow air underneath to cut down condensation, they have not damaged the paintwork as they are very light.
The light covers are rotated according to the weather forecast and are dried on low heat in a tumble drier. You cannot do this with a heavy weight cover.
With the hood up i have found the heavy cover scuffs the Mohair fabric on the roof frame as it shuffles about in wind so i keep the hood down mostly.
The biggest problem is from condensation under the covers so there is often a small pool of water on the tonneau cover after heavy rain, not too bad though.
