best advice - download openscad and run through a few tutorials.
Something like that is pretty easy to do in openscad.

And with a case like that, it'll need to be custom fit to your car - so expect a fair few iterations before you get a perfect fit.

That could work out expensive and as we don;t have acccess to your car - it's doubtful the first attempt would work.
Also i don't have a modern rpi to hand for measurements either.

And it's not going to be your last project. So best advice, suck it up and learn how to use openscad and make your own models :-)
http://openscad.org/

Once you get the basic usage - it's a surprisingly quick learning curve.