Tempered glass will explode into to tiny pieces like a car window, it takes lots of abuse. I,ve installed atriums and had to walk on the glass itself to erect, the first time was scary.The wrong place to tap it is on its edge which would be protected by the frame you make. I personally would go with the lexan. You could cut it yourself and then just drill and counter sink, Use Brass or Stainless Screws, and just face mount it to the hinged ,prepainted wood. For 100% watertight fit use a bead of GE silicone around perimeter and let it oose out,let dry and you may trim excess with a razor. We did this to a commercial fishing vessel we were rebuilding and it lasted more than 15 years than we sold it. You might want to take the sharp edge off with some sand paper. Nothing more satisfying than a job well done yourself.