Another vote for Ultimate car coversUltimate car covers. I have used these for several years and are superb. I have used one outside for the last 5 years and although it has discolored a bit, it has not degraded or worn at all. The only issue I have is with the sizing. The first one I bought fitted absolutely perfect (it was specifically for a 240z). The subsequent ones have all been too big so i have returned them for a which were still big.
Satin Soft Stretch Indoor Car Cover - Morethanpolish Ltd
If you have a tricky angular classic or vintage motor these soft, stretch indoor car covers are ideal and they come in a choice of 6 sizes and 4 colours.morethanpolish.com
I bought this (as recommended by people on the Forum) Size SMALL is a perfect fit and I'd definitely recommend it too.