Scottie,
Don't know if the filler is race legal or not. But I got tired of having to open the hatch every time I put gas in the car, and if I spilled a little, then the fumes were inside the car. I made the hatch when I made the rest of the body, so it is fiberglass. It uses the OEM hinges, but I use Dzues fasteners to hold the end down (this was originally race only, and was held on only with the fasteners, but I have since installed the hinges and removed all but 2 of the fasteners). The Lexan is pop riveted in, with a small thin bead of sealer applied first. The size was reduced on the window so that the Lexan would not get hot and sag on those hot summer days (the Lexan may not have done this anyway because of the convex shape when installed, but I did not want to take any chances). The total weight of the hatch is 19 lbs. It's not real light, but I was looking for strength and longevity along with a weight savings when I built it and did not want any future warping to take place. As it turned out the rear (IMHO) took on a different and better look with the smaller rear glass. The window sizing was done when I made the hatch originally; before Hydra got me thinking seriously about the filler idea. I could have gone further south with the filler, but I still have the spoiler to re-install after the paint job is finished, and I needed to be sure it would clear it.