Back to the OP's question. I have a Guardian Weatherall Plus cover by Dowco. It is awesome so far as holding up to sunlight and very well constructed. My bike sits outside all the time, so I need a good cover. Dangit.
The only challenge is keeping the condensation down. I am trying to think of a way to put a little fan under there to keep it dry. Maybe some dryer vent and an attic style fan? Anyhow, the cover is great and they come in many sizes and configurations. Get them direct or at Revzilla.