BTW, those grain cars look REALLY good, awesome weathering!
I should also mention that I have used this stuff on HO cabooses for the Red reflective tape above the doors, I was able to color it with just about any color of Sharpie and it would still come out looking awesome.
I did find 1 GP38-2. An old athearn unit I did probably 15 years ago when I was still a kid. The last pic is of the tape I use. I wish I knew the company that made it. Its VERY thin..I would say about as thick as clear masking tape. Its is also flexible and it weathers pretty nicely too. I only wish I could figure out a way to place a decal over it so I could make the CONRAIL QUALITY nose lettering reflect!