A little rain isn't going to hurt it, just plug your exhaust, the sun will though if you don't keep a good bit of wax on it as well as keeping the seats coated with something like armor all. I've heard similar things about tank bras and causing more harm than good. I guess it would come down to how often you ride it. If you ride every day, then a cover would be a pain, but I couldn't see moisture or dirt being a problem with it since it would be removed alot. Over longer periods of time, a few weeks, then maybe. I do know that some covers have a one way membrain on the that allows moisture out, but not in. Just what I've heard though, never needed to test it since I have a garage at the moment.