IMHO I cannot recommend any bike cover....Just to be controversial and excite debate
Used to leave my K100RS outside all of the time in all weathers and no probs whatsoever- till I purchased a canvas type cover and immediately rust started appearing overnight.
I reckon any covers keep relative humidity and heat extremely high resulting in rust. I would need convincing that the latest fabrics are any different.
I tend to use the cover to keep prying eyes of my ride as I live on an estate where there have been bikes nicked or vandalised. I know a cover dosen't stop it but it makes me feel better knowing its covered up when i'm kipping.