I've been working on this project for about 4 years now, and havent made any noticeable progress. So I've decided to simplify the project a bit.
First, I've rethought how I'm going to mount the screen in my dash. Instead of popping a mold, modifying it, and casting a whole new dash bezel, im going to use the original part and modify it with fiberglass. The solves several problems, e.g. mounting, fitting, steps involved, types of materials needed, etc.
Secondly, I will not be mounting an Android tablet in the dash, and instead I will be installing an LCD connected to the RasPi.
Lastly, audio will be simple Bluetooth audio that feeds the amplifier instead of a USB interface connected to the tablet.
I've already made progress on the fiberglass work.
It's a little rough at the moment, but I'm working on it. I'll writeup another post on how I made the dash piece once it is complete.
Hopefully with the project being a bit less complicated I'll be able to make real progress on it in the coming months.