I've used Sullivan Carbon Rods with tubes. The tubes are supported at each of the formers and at the exit point with epoxy.
I have a method that I use on them all to secure the steel rod at the end of the carbon rod... I mark the steel rod for depth of insertion into the carbon rod, making sure that the depth is well within the tube and within the fuselage, then I secure the steel rod with the chuck of a varriable speed drill, I then coat the steel rod with CA and immediately push it in the carbon rod while the drill is quickly turning, and don't stop until I reach the mark where it is supposed to go and stop. Once I stop, though, the CA is set and it is NOT coming apart and makes a real light-weight and strong push rod.
I have this set up on my Venus II as well as my Tiger 120. My Excelleron 90 has pull-pull for both the elevator AND rudder. Nice, but there is quite a bit of cable going back there...
CGr