I back-drilled the two antenna back-plates to the fuselage skin, using 11 additional holes on each plate for attach rivets, and four holes for the #8 screws that actually attach the antennas. I also marked, drilled and countersunk the plates for four nutplates each. Next, I masked and stripped contact patches inside the fuselage skin for to provide a good grounding surface, using a sanding disc to remove the paint. The attach holes in the skin were dimpled with a pop-rivet dimple set. The stripped patches and the backplates were alodined with a Touch-N-Prep pen, then I riveted on the nutplates.
All that remains is to rivet the plates to the skin, and the comm antennas will be ready to install when the time comes.