if you get a decent one they can.
but they have to be a decent one that's a proper fit so it wownt blow around and cause swirls in the paint and needs to be removed to let it air out etc periodically.
two lads I know have them for their Porsche 911's which comes out once a week if there lucky for about 4 months of the year, the other 8 months its sat under the cover, and has been like this for a number of years and is still in immaculate condition. I think theypaid upwards of £150 for there car covers though.
as said though, unless you remove them periodically to let them air out they can damage the paint, it can also damage the paint if there not a proper fit or made out of cheep material.
sadly I don't know what is a good material and what isn't or where to get a decent fitting one.
if it was me though, id just wash it, put a decent coat of wax on then every few weeks take it on a quick run around the block so that nothing seises up and then wash it again.
