This is what I did for the fairing at the TE of the wings.. this fairing is supposed be be attached to the wings, but I figured it would be more robust if attached to the fuz. I. made up a 1/32" ply guide to the desired shape, and glued that to the fuz ; added some wire reinforcements as a form of micro-rebar
then piled in the aeropoxy which I then shaped to suit.