I have a DuPont Tycvek cover for mine. It's breathable, and fits pretty well and is secured by a couple of elastic ties (make sure they are fairly tight or the cover may come off in the wind!). You can get them in Halfords for around £70 - £80 depending on your car size (IIRC the Crossfire is a medium).

They are a metallic silver and can make your car look like a baked potato when on.