I had the material made .375" thick. It looked about right to the photos I have of the full scale. The thickness is one of the keys to getting the look, as the very thin wire screen mesh generally used, just does not cut it.
It is important to remember that cooling is more about exit air evacuation, than entry air. Flowing the air over the right areas, and then getting it out. There is a ton of exit area behind my engine, but I may look at making some of my louvers functional. The shape of the louvers actually create low pressure, and are perfectly suited for this task. Of course we shall see, but I am pretty confident there is enough air going in.