Mounting Leaning post

[Bushwacker]

If deck is cored, you might consider drilling oversize holes (like 1/2" for 1/4" holes), fill with thickened epoxy, then redrill and tap for machine screws. Toggle bolts are another option. Sheet metal/lag screws don't hold too well in glass . . . the threads are sharp and tend to cut into the glass if there is any relative motion.