Hey Charmo, do you have a pic? I'm not sure how you are doing it, but I usually silicone my frames and glass together before I start, so it has good sturdy framework...When You put it in the frame will you be siliconing it to it? Once the grout is in, it is like a mini cement puor job and should make it pretty solid and so the only concern I see is if the wooden frame isn't sturdy enough to help with keeping it from shifting around...not sure if I'm helping or just rambling....I'm so bad with out pictures to see...

OK Here are some pics to show you what I mean.
One pic is the GOG itself and the other is the frame and backing. The backing is not made of wood although it is thicker than carboard but still flimsy, however if I glued it right to the back of my GOG wouldn't that make my glass study enough for grout? Remember it won't be placed by a light or window so I don't need to have light coming thru.

Here is the picture of the frame itself as well as the backing.