I used black stocking material as it stretches easily with little force. The plastic tweeter mounts are part of the mounting kit that came with the JL C3-650 speaker set. I used small bull dog clips to hold the cloth in place as I stretched it over the mount and behind the panel. CA (Superglue) was then applied around the tweeter opening and edge of the sail panels and then sprayed with activator to set the glue. Surplus material was then removed. Three layers of CA were then applied to the stretched cloth to form a light and strong surface. I didn't reinforce the inside of the stretched cloth as the sail panel can be installed without distorting the structure.
I used plastic bumper filler to smooth, followed by plastic primer and finally Plasti-Kote super matt black. Photos show the fabrication stages The fit and finish looks OEM which was one of the goals.