Rings made from plastic pipe sound like a good idea!

I was thinking about putting drops of super-glue in the crease between the guides and the wall so that the film won't slide around. I wouldn't be able to slide the film in against the wall of the drum, but I don't do that anyway, since I was getting badly scratched negatives. Instead, I bend the film away from the wall, move it into place, and then push on the center of the sheet until it snaps into place.