I made a sunroof delete plug for $65 a few years ago. I don't think it is an absolute requirement to vacuum bag the fiberglass. On this one I laid a piece of shrinkwrap over the sunroof glass and applied 3-4 layers of the thick woven mat. Just be sure to rotate the mat orientation with each layer for strength.You'll need to make some tabs to hold the new panel in, which may require some welding. The final product needed sanding on mine, but after finish work and paint, this is what I wound up with:
Use an ice cube to smooth the silicone seal. Mine looked rough because I screwed the first seal up doing it the wrong way and had to do 2 plies.
Boy did it make a difference in handling though. Remove 37 lbs off the highest point of the car and see what happens.
This integra weighed in at 2320 with a nearly stock appearance.