That would work. You could clamp it in place and drill 3 or 4 holes through the flange to run bolts through. Once the holes are drilled, you could put the bolts through the cover, and weld them in place, then stick the bolts through the holes in the rocker flanges, and slide on a washer and spin on a nut for each bolt from the back side where access is easy. You might not want that bottom bend to be quite 90 degrees, so water that might get in there can run out. I can't see how far under the pipe that bottom piece is, but you might not want it too wide (maybe about 1/2 the diameter of the pipe wide), the heat could escape better with a narrow bottom flange. Paint them with high temp paint, they could get hot through the summer.