the best car covers IMO are the Specialised ones
www.carcoversuk.com
Ive got the 3 layer breathable jobbie - they fit like a glove (fully tailored to the S2) and you can put them on when its wet/engine warm without issue
I dont have a garage and use it during the winter when its snowing or frosty - saves a lot of time in the morning defrosting the car. Also it keeps leaves and stuff out of the front/rear compartments