I didn't like the idea of drilling holes in my cowl either, especially at the lowest point were water will pass by. So, I made a "hat" for the opening out flat sheet metal with a bent over lip around the edge. I drilled a hole in the center and installed a 3" bolt with nut sealed with RTV. With a slight bend across the middle, it fit up through the vent hole and settled out on top. A piece of flat bar across the bottom with another nut tightens it down and holds it in place. Then it was sealed with T31 RTV that I used on the engine. I thought I took pictures, but can't find them. One of these days, they will turn up.

With the bracket, I drilled the holes up as high as I could get them without fear of going through the exterior sheet metal. This location was less likely to see enough water to cause leaks into the interior. Sealed it with the same T31 RTV. I bet the black would work just as well.