1. With tail fixed, temporarily fill the space with stiff foam and carve/sand to a nice 3D shape. (The foam is lightly glued to the boom just enough so it won't move.) It doesn't have to be perfect.

2. Remove tail surfaces, and cover foam with a couple of layers of light glass. Cover the boom with something so the glass won't stick to it. It's not clear in the photo, but this fairing is continuous across the top - it's in one piece not two.

3. When cured, remove the foam/glass, chew away the foam then add a couple more layers of glass on the inside.

4. Epoxy the glass permanently to the boom.

5. Spread on a coat of any filler, prime, & paint.

You see in the photo the curved rectangular space above the taper pins which you have to close with an access panel. I had it slide into a slot on the front of the tail cone and then screwed down with two bolts that went into captured nuts on tabs attached to the top-rear of the fairing. The hole above the front spar plate gives access to the front spar attach bolt, of course, when the tail is rotated up.

As long as you have a folding tail mechanism that works for you, this tail fairing (or something similar that you may make) pays for itself many times over, in time, hassle, and tape.