The cover that Philip Blair told you about, and the one that I use (have two of them) is the Geza cover. They are not cheap, but they are well worth the money. PBlair had one custom made to fit his F6B. I have an older one (yellow label) and a newer one (white label) and I use both of them when stopping for the night. The newer one goes on first, and then the older one covers that.

They pack up easily, and are very good at keeping most things out. They are not 100% waterproof, but few of them are.

To me, it is worth the money. http://www.gezagear.com/