I have seen something like this for RZ and 645 but not for RB.... Is there such thing as back FILM BACK COVER for Mamiya RB-SD? Behind that thin stainless steel darkslide is a delicate film, and the mating surface of the back is what seals the light from coming in. I'm thinking it makes sense not to casually toss backs into my carrying bag. How do you carry your back? Carefully? Casually? Don't care?