Worse thing for you car mate, car covers.
I have my car detailed & colour corrected once a year by a guy the knows most things about car care and he says you are 10X better off leaving it out in the open opposed to putting a car cover on it.
Mine is outside most of the time and I've never put a cover on it.
If you did still want one Halford do one (large) that fits ok.
The medium size is not large enough to cope with the rear wing.
