Boat cover that attaches to the rub rail

Sorry I dont have any photos so you will have to use your Imagnation.

A friend of my'n was talking about a boat cover that coverd the interior of the boat, It didnt use snap's or buttons, It was a cover that you could tow with that would keep the dirt out of the interior of you boat. He said it attached to the rub rail and has some sort of straps that would tighten it up, I have seen photos of cover that cover the interior of the boat but nothing that I would use because it used buttons all the way around the boat, Have you seen the cover Im talking about????
I dont know if this boat (photo) uses that type of rub rail attach system like im talking about
but its sort of what Im looking for, This cover looks like it might be to loose to tow with??