I decided to tape off the bottom edges of the inside of the car body before painting so that there will be two unpainted sides touching each other when the underframe is installed in the body later on. That way the glue will be bonding the resin parts rather than bonding the two paint layers.
I followed the instructions exactly and bought a bottle of Polyscale's "Special Oxide Red". I mixed it 30% paint and 70% isopropyl alcohol. I had no problems airbrushing the body and the two doors (done separately). I had never used Polyscale paint in an airbrush, and this was my first time ever airbrushing a car body. I am quite happy with how it turned out. The paint dried quickly, so it was easy to keep adding thin layers of paint. Also, the paint dried flat not glossy. I airbrushed the inside of the car the same color. I have not yet decided whether I will have the doors opened or closed on the model, so I painted the inside in case I decided to have one or both doors open.
I let the body dry for several days before I moved on to the next step.