Phil, have you ever tried (in addition to the technique you described) attatching an approx 50cc syringe to the drain plug hole(ie, using a hypodermic needle through a cork) and applying a little bit of negative pressure on the hull to draw in the epoxy and evacuate the internal bubble? You wouldn't want to be too agressive and you'd need to get the viscocity right or you'd suck some epoxy into the inner hull...

Have you ever used threaded inserts into epoxy? These are really interesting; they require slightly larger holes but provide a much stronger attachment and the screw can be inserted and removed without degrading the strength as I think might occur with a screw into an epoxy hole. I think some inserts can be epoxied in place without having to tap. I don't know if it would be possible to tap an epoxy hole and even if you could you'd still need to apply a thin coat of epoxy or adhesive silicone prior to installing the insert. Just food for thought.

In general, when do you epoxy a hole for a fastener vs put in a backing plate or SS washer?

Jerry