I did say it was an ambitious plan. I should add crazy and with a low chance of success. Anyway I was thinking to try Yupo. They make a clear or translucent version. It is a bit stiffer than photo film, so I'm not sure how well it's going to behave on film spools. However it is used for carbon tissue and seems to hold emulsion well. Anyway, I'm not that far ahead in coating, so I've got loooong ways to go before worrying about specifics.