ORIGINAL: wabi
I hunted with it on our opening day of gun season in heavy rain and simply used a nylon cover over the action (an old folding camo chair bag made a good cheap cover

) and a baloon over the muzzle. When I finally saw a deer I simply slipped the cover off the action & scope, cocked the rifle, and BOOM! No problems at all!
Heavy rain I use this and put Saran wrap over the breech area. They fold up nice in your knap sack and only cost about $20. Chap Gleason