[realcoray]

My dad does upholstery work and he suggests on these cars that you start with the upper metal part off factory panels (I see it's mentioned in the last post in the thread). On some cars that wouldn't apply, for example I think early mustangs are basically a flat panel with no upper part that covers up that ugly area at the top. For a Nova, you'd want to start with the metal.

I believe he uses Luan board then foam and then the materal, already sewn into whatever pattern. You can use less or more foam in areas to give it dimension or to account for things like the door handle/window cranks, and also in the area for an arm rest.

For something closer to what the aftermarket has you'd probably build up a complete mold out of hard foam (like the green garden foam), on top a door. Basically building a mold for the panels. There are a lot of fiberglass websites that detail how to create a mold that you can use to make a part. You'll understand why the aftermarket fiberglass door panels are priced the way they are pretty quickly this way.