In the past I have put a small amount of glue around the outer metal edge of the frame just next to the gasket. I do not make any cuts to the material around the windows. Once it is secured with the glue I put on the garnish molding and tighten( just snug) it down. I then use a razor blade or razor knife and go around the inner edge of the molding and cut out the window openings. A word of caution, be careful and use the proper length of screws for the garnish. Too long of a screw can go in and touch the edge of the window glass and cause it to break. Learned that lesson the hard way.