After a quick Google for G10 I believe this to be what I would call FR4 glass fibre as used by PCB manufacturers? I can see why you are worried about the dust. As it is eminently glue-able, why not make this in two pieces so that you have downward facing flats to fix to the bed and holding it down accurately becomes easy peasy.

Alternatively, if you are CNC'ing it, leave pillars on one side to support it when you turn it over. You are going to be sanding it down anyway so pillars are not a problem, you can even drill and thread.

Have you considered aluminium alloy, it would be a lot cheaper and in T4 temper, probably stronger.

I should warn you, everyone hereabouts waits for me to put my foot in it before they chime in. They don't like to go first. Better advice will probably follow.