Drew an outline on the inside of the fuselage walls for NACA ducts I purchased a kit from Vans. It was a great deal. High quality and complete..The entire kit was far less expensive than just the vent fromACS. I highly recommend it. The kit came with a paper pattern so that you could lay out exactly where to make the cut. It looks crude, but it worked like a charm. It required time and care in the placement so as not to interfere with the cowl cheeks. I also rivited 4 trim parts to the outside of the fuselage side walls.
