You may have a hard time finding this. Looking over my collection its hard to determine what material the blankets are made up of using the old photos. Washed out lighting and black and white color makes it difficult to determine. I see what looks to be a gum blanket being used to augment a tent cover for water-proofing in a Union camp photo but it looks like a wool blanket too. Also, photograghy at the time was just not possible on cloudy, rainy days, (when they would be used) so having these rubber-water-proof blankets out and in use on sunny days would be rare.

David