Personally, we'd opt for just keeping it clean and dry - however, if you're keen on covering it then make sure you get one that's a tight fit, try and avoid 100% waterproof non-breathable material like tarpaulin as it allows the car does stay damp leading to moisture, watermarks, micro-blistering and other non-fun stuff. It's the same deal with cotton, which absorbs moisture. Even if you get a breathable cover, it needs to be removed in periods of high humidity or long spells of rain to allow the moisture to evaporate (this also applies to heavy snow, which won't allow the cover to breathe). Try and get a breathable, semi-tailored item. And don't forget - only use a cover on a clean car as any dirt could potentially scratch the paint. We'd recommend the Halfords all-seasons car cover, but it pricier than a lot of the alternatives you'll see on Amazon. The Oxgord car cover is also well-rated.