About the sanding… I patched the controller due to the Vintage Air controller, and the AC-Vent due to a screw up cutting it (got mine un-cut). I had to build the opening up with scrap from the cutout and some POR-putty I had laying around. I then used regular body filler to finish off the patch areas and a few low spots. If you have high spots, you can sand them down. Then use finer and finer grit paper until the scratches are gone and it’s smooth (it will be hazy). I put 2 coats of paint on, then sanded some more areas I was not pleased with, then applied 3 or 4 more coats. The paint build up fixed a few areas. I bet you could use a high build primer to it really smooth! From what I understand, and someone can correct me if wrong, once you plastic prep and get the first coat of paint, you can forget about it being plastic, and apply any paint product compatible with the product initially applied over the plastic prep.
On the signals, still thinking about how and where I want to mount the led’s. You’ll probably come up with something before me, so let me know..