I think the coolest horns is just a piece of tubing through the elevators. Pick up a roll of Spyder Wire (Kevlar fishing string) and do it in a closed loop configuration. The tubing can be aluminum and just big enough for the string to fit through. It makes for a very light control installation and I have used closed loop for years in big scale gliders.

Just keep in mind the less you put in the tail the less you have to put in the nose.

I am sure the answer to your question is to put them on the outside (lower surface)as it would get a little tight on the small HLG to put them on the inside (upper surface).

Let us know how you make out of if ya need a little more help.

EC