I have decided it would be a good idea to put an air damn just in front of the air exit on the cowling for my Extra to get better cooling for the DL. I have seen Pe Rivers articles on this subject but I am left with one question. What is the best way to build abd attach it? I have some very thin aluminum sheet that seems like it would work but I am not sure how to attach it to the cowl. Should I reinforce that section of the cowl with balsa or lite ply and just bold the air damn on? Does the reinforcement need to be glassed in?

Thanx in advance for any suggestions.