I see. Interesting. I remember Mercedes-Benz, I think it was 2-3 years between 1975 and 1980, they used a special undercoating that was like some kind of plastic. It was sprayed on, and did not stick for whatever reason. And oh my goodness did those rust. Very few of those has survived in Norway. People had a horrible job getting the plastic stuff down, and repairing the body, and re-coating it with primer and paint and whatever they put on. A disaster on 4 wheels. The thought was good, but theory and practice is not always the same.
Bill