Andy, You do know that glass is made from sand? I would guess there is going to be small shards left behind that would dull your tools just as sandpaper, but that is just a guess.
John, Interesting build. You are putting alot of craftsman ship into the decoy, and I appreciate how you are working around using the tools you already have. On epoxy , I use West Systems, it is a great SYSTEM of epoxy, hardners for differeing conditions and additive, which I have found to be stocked at the local West Marine store. I started using it long before I found the internet and all the alternate mail order places, and used it to build a canoe which took alot of epoxy. I have been using it since for decoys, paddles, and other household projects, and although there are many cheaper alternates out there, for the volume I use, I don't see a point in switching. If I get to building another boat, I would think long and hard about what brand to use, but for the small amount I go through it is easy to stop in the local store and pick up whatever I am in need of. I noticed lately that the local Woodcraft branch is now stocking System 3. Personally for the quantity your likley to go through on decoys, I'd look to pick something up rather than ordering it and having it shipped, but that may be just me.
Chuck