What was the original color of the tank car? It appears as if a blood red color was painted over it but it’s hard to tell. Ideally look for photo’s of tank cars and try to copy them as best you can.
I usually use a dry brush. Load up a brush, wipe off just about all of the paint, and then paint the car with the brush. There are a couple of web sites that go into a more detailed explanation of dry brushing.