Chief Car covers here in Western Australia sell a fully fitted one in tailored cotton for $375 and a water repellent one in a type of canvas for $579. The boss reckons he's done a few RS500's over the years and a couple of saphs so has all the templates.
They seem to fit really good so I'm going to take a punt and order the water repellent one.
They have been in business for over 20 yrs so I guess its worth a gamble.
I'll let you know in a few weeks time when it arrives
Cheers
Keith