What material to use for non metalic pull-pull setup?
The antenna in my Balsa USA Eindecker shares the interior space with 6 steel pull-pull cables.
I have several planes with the antenna and pull-pulls in the same space.
I use the DuBro pull-pull kits, and also .012" control-line flying wires.
If you're really antsy, Sullivan makes a Kevlar pull-pull setup, which I have also used.
I set these up with the coupler (makes no difference which type you use) at the surface rigged to permit taking up as much slack as possible before flying (maximum number of threads available to tighten the wire), as the flying loads will "bed" the cable run better than you can do it before flight.