If the plane has an existing mid fuselage opening, such as with some electrics, I'll frequently run the antenna on the outside of the plane along dark striping.

Scotch or clear tape holds it in place and the dark striping makes it all but disappear.

Once it reaches the tail I run it up or down the rudder being careful to keep it away from any linkages or areas that it can get entangled on, and again affixing it with clear tape.

This prevents the scratching of the wire covering that occurs if you leave the wire merely hanging out.