What lshick said makes sense to me.
The accepted way to do the fix is to do the following:
Lets say you have a 1/4" bolt.
- You drill a 1/2" hole through the top layer of glass only.
- Put a 3" nail in your drill motor and bend the end of it about an inch, 90 degrees so you have a hook. Use this contraption or whatever other method you can think of to hook out the core between the two skins.
- Tape the bottom
- Fill the hole to slightly above level with epoxy thickened with high density filler.
- Sand
- Drill to 1/4 inch. Bed the deck fitting with boat-life 4200 not 5200.
Now you have a solid plug of epoxy with a hole in it. No water can get into the core. The re-bedding may have to be redone every 10 years or so but at least their will be no core problems.
Things will move no matter what you do. The goal is to control what happens. Your idea of trying to prevent things from moving will eventually fail anyway.