I know I’m on the wrong coast but I had one made by a local shop. The snaps are under the rails so I don’t need to clean around them. Welcome to the club!
http://club.benningtonmarine.com/threads/travel-cover.8300/#post-110932 try this thread. This one was made as a travel cover. But you could go with lighter material to get you what you want. If it is a stationary cover you could have it designed to cover down to the side rails and over the motor. I used mine as a storage cover in doors in the winter too.