Hi Rob,
If you are woried about damaging the glass around the bolts you could always make up some crush bushes. I guess that's what you'd call them?
The floor of my CR has a foam core between 2 layers of glass. Very strong construction over all but weak when you bolt through it as it's easy to crush the foam core. I machined up these bushes for my seat mountings which also hold the body on. They sandwich the glass in place but dont let you over tighten it and crush it. They also provide a solid connection between the seat base and the chassis.
Cheers