This is a pretty simple model, but maybe it'll save somebody some time. Every Cambo camera I've seen has a small cavity with a sliding flange in front of the ground glass (for attaching a reflex finder or other accessories). This sheet will fit almost perfectly into the space and will be held secure by the flange.
So far, I've tried it in a Cambo Wide 470, a Cambo Wide 580, and a Cambo Cadet. It worked perfectly in all of them. I used it on a recent trip where my camera was stuffed in a backpack with some Grafmatic film holders and lenses and the ground glass survived the trip intact.
The author marked this model as their own original creation.