W220 LWB Car Cover (Non-Scratch) Recommendations?

[cheekster]

I'm in desperate need of a non-scratch waterproof car cover for my S320CDI LWB (W220) as where it's parked outside on the drive, there's no garage or overhead cover and within a day or so of washing it, it's covered in dust!

Any recommendations for something cheaper than the £145 ish one from Mercedes?

Thanks.

Cheekster.