I install a pushrod tube inside the fuselage. If necessary it exits near the other push rod tube exits at the rear of the plane.
To make sure the antenna does not crawl out of the tube drill a hole through the tube close to the end, cut a slit from the end of the tube to the hole, slip the antenna through the slit into the hole.
Rough up the surface with sand paper and use a little medium or thick CA to secure it front and rear.
I use push rod tubes large enough that I do not have to struggle when I thread the antenna through.