Winter coverage?

[Jonzo]

Hi guys, wonder if i can pick your brains once again (Cue micro-surgeon!). Now that General winter is arriving with horrible rain storms, i want to buy a decent cover for the odd night when the poor car has to sit out on the drive in all sorts of shite weather, but i dont want to spend a fortune on one in case some 'orrible little so & so's run off with it. I was looking at the custom jobs that Halfords sell (ie the Tyvek'? range)...any recommendations/warnings about where to get a waterproof cover and how much?
cheers
Mark.