Well, here's some night photos. I used software to brighten them up.
It's not exactly what I wanted to accomplish but I guess it's good enough. There are imperfections in the surface, the coroplast's corrugation is still very visible, the screws are not neat and are pulled in a little, and the edges can be seen from some angles (and aren't straight). All in all, though, I think it won't be noticable from far away, and most people won't notice it up close either. It may look ok enough up close for people to think it's an aftermarket product that I bought.
You can see my truck in the background of one of the pictures, with its grille completely removed. That grille is indoors where I can work on it without being out in the cold. I had all day to work on it and didn't do much (I attempted to mark and cut a template of cardboard and got discouraged).
While I was mucking around with grilles, I turned the VW logo upside-down.