The milled fiberglass arrived today. I got it on eBay from FiberGlass Coatings, Inc., a pint for about ten bucks, shipped.
Yes, I put on the hands of blue (need more of those, too), and a mask as well.
I wasn’t able to find any information on what epoxy/fiber ratio to use other than “enough to get the consistency you want”. I went about 5:1 by weight with the Bob Smith 30-minute epoxy. Still thin enough to self level but not drippy. I also had to guess at how much to use, and what I ended up with looked like probably thicker, heavier fillets than I need, but I didn’t feel like trying to remove half of it.