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.
that's really nice. It's funny how much it changes the look of the car (especially with the badge turned upside down). If I saw it pass me on the road coming at me I wouldn't know what it was right away.
Best fill up so far is now 29 MPG!
Ok, finished both and got daytime pics. They don't look as good as I wanted them to. Up close they look kind of hacky and shabby. From far away they look fine, so that addresses half of my concerns -- one being unwanted attention from traffic cops, the other being a matter of looking professional when I arrive at work or at a job.
I struggled with the decision on how to mount the one on the truck. I had previously made some cleats that I would screw to the grille and then screw the sheet to them, I considered using silicone, and finally decided that 3 zip ties ought to do the job easily while being very easy to reverse. This turned out to be a good decision, because it won't last long. The material is too brittle. A piece broke off while I was cutting it, but luckily the sheet was large enough to re-mark and try again. When I was tightening a zip tie, another piece broke off , but it was too late. I'm sure the end with the broken hole will crumble while driving.
Apart from the shoddy workmanship, the one on the truck actually looks nice (but will be visible from far away and grab attention). In the close-up of the broken bit, you can also see my shoddy edges and how they're not quite held flat against the grille. My plan was that they'd sit against the indented chrome edge that appears made specifically for the purpose.
trace the GMC with a sharpie and cut it out so that it sits flush against the grill surface. it will be less noticeable that way but that one would take some time. I did something similar on my wife's element but hers is a much simpler shape to cut out.
I also heard that hers reflects the sun really good if the sun is going down infront of her, she could potentially blind the person in front of her.
Be the change you wish to see in the world
I thought of sinking it past the GMC but it hadn't occured to me to cut it to the shape of the letters -- I was going to just cut a rectangle.
Due to the shape of the grille I might be able to re-use the piece and lose the broken bit, where it would lay flat against the black slats is a smaller area than where it is now. I don't think it's enough, but it might be. It wouldn't be as aerodynamically good as it is now though.
More on the construction of it:
I gave up trying to template it in cardboard and just traced it with a dry erase. Then, I cut it with a cordless circular saw (as suggested by someone else in another thread). After cutting caused the first break I turned the blade on the saw backwards, which helped. Also, I was cutting it on a wood surface so the wood would stabilize it. On the second try I screwed it into the wood to hold it perfectly still.