Re-dustproofing a car dust cover

I've had my Moss, indoor dust cover over my TR6 for many years & it still looks as good as new. It's been cold washed using no detergent many times over the years but this seems to have reduced it's effectiveness in keeping out the dust & I've increasingly noticed the car gets covered in very fine dust particles when left for a while over winter. These are obviously so fine they are getting through the fabric & onto the car, anyone had this & know how to restore the cover to it's

Thanks to all for the suggestions, after a look at several, I went with Ken’s (Poolboy) recommendation & bought an Evolution premium edition cover. An internet search quickly found a supplier with a UK website without any problems & I ordered one after being offered an additional 10% discount. It actually shipped from Stafford TX US, free postage by Fedex International & arrived just 3 days later. If I’d realised it was coming from the US, I probably wouldn’t have ordered due to poss