I like your project, and I was thinking of building something similar. But I was planning to use lathes (I don't know the exact name for that) that you may use to mask gaps between two different floorings (see the pic). Those can be used easily with the rotating shaft, just glued to the spouting (again the naming
) at the bottom side. Made from aluminium are very light and strong so it can be used even for external grill blocking. These are comming in various sizes and colors, and it can be easily repainted to any color needed as well. Drawaback of this solution is that you have to use more of them to cover larger area, since these are mor narrow than your blinds fabricated of coroplast. But they will stick closer to the body so maybe it's not a drawaback at all. Depends on what type of grill shutter you are planning to build, internal or external. I was thinking of building that to block lower grill in Berta, in opened position it looks almost like a factory grill, in closed position is smooth enough to give good aero shape.