Gazza
Get a car cover from Repco, about $60 or $70 for one that fits a Rolls Royce. They are water proof and they breath too. The ones I use are the blue ones. Let me know if you want more info. A mate of mine had one of the expensive ones that lasted a couple of years and then was stuffed. If your going to replace it every few years might as well choose a better priced one IMHO
Cheers
Chimo