Hey Loren,
They way I’ve dealt with putting holes in the deck, even a screw hole…I drill over sized holes but only thru the top layer of glass. Then use a bent nail in a drill to remove the core around the hole. Vacuum the core fragments carefully and fill the hole and areas where core has been removed with a thickened epoxy paste. Leave it sit over night and then carefully drill the proper sized whole through both sides of the deck. Bed the fitting with your choice of bedding material and no matter what happens with your seal if the fitting should leak the water can not get into the deck cores, it will simply leak through the deck and you’ll be able to spot it, fix it with zero deck problems. Cheers, Robert