In this case I used all sorts of things. The lines are scored in by cutting them first with a hacksaw to make sure they'e straight and then with a jigsaw blade if I need to make them wider.
For the back of the neck, I used scrap bits of styrene and PVC sheets as well as some textured plastic bits I had on the bench wherever I needed to build anything up. For the recessed parts, I was carefully whittling it with the X-acto knife and/or Dremel tool. Once the bulk of it was done, I went over it and puttied up all of the seams and then sprayed it with a couple coats of "truck bed coating" to give it all a matched texture.
I haven't taken any pictures of it since the truck bed coating.