I have done fake door panels before, but I used a 1/4 sheet of mdf. Instead you want to use abs plastid as there will be moisture in the door causing the mdf to swell up. Also for the arm rests, you can use some foam type stuff, attach that to another piece of abs plastic the shape you want it, and sand the foam to the shape you want it and wrap in in what ever you like. You will also need some vynil to cover it up, or if you want to paint it you can do that. Also if you want the abs plastic to bend to a shape, use a heat gun, but do this in steps and have some water to cool it off instantly, its a really hard timed process.