Great design - good for you for trying some difficult stuff. I would smooth like crazy from the outside and fill like crazy from within.

Firstly (where you are especially worried about sanding through), I would drill (DRILL!) tiny holes(1/32") all over but in very carefully located places that you can replug later w/ dowel or whatever (my guess is dark wood better than light - but test it first) and then I would lightly glue fluorescent paper on the inside. Then if you get really close to sanding thru you will notice how thin you're getting by the coloured dots gettin' real close. My guess is that you could get up to 1/32" in places with not too much worry (fill on the inside or more glass).

Any how please tell us how you dealt with this problem because I for sure am gonna need some good advice on this problem too in the near future!!

-mick