I have done three sets of flush mount directionals on streetglide fairings, but have yet to do a roadglide.
It is the same process though.
Measure and cut your opening to fit the lens.
grind down the inside of the fairing in order to have a good sturdy spot to epoxy in the lens, and build up the epoxy to meet bck up with the inside of the fairing (like before the holes were cut).
Just o not cover the lense with epoxy.....just the mounting edges.
the lens will extend out beyond the outside of the fairing.
sand down the lens until it meets the outside of the fairing, and matches the contour.
I epoxy two threaded studs, to which the led housing will bolt to on the inside of the fairing. (that way you can remove the led housing if they happen to have a couple led's go out)
the process is actually quite simple, it just takes time.