I'm doing a project to decorate a car with cast-on details, including grabs and ladders. The car is silver, but the grabs, ladders, and a few other things should be black. It's N-scale, so masking is problematic for things like this. I think I can do a decent job by painting the car silver then doing the details with a black Sharpie. If that works out, what's a good clear-coat to seal it? I recall that Sharpies are alcohol-soluble.