The electrical properties of sealing materials and greases are not defined
or specified. They probably make poor dielectrics when surrounding or are in
between transmission line conductors. I wouldn't use the stuff. A few
spots of super-glue would be ok.

There's no need to run open-wire line through walls and windows via two
spaced holes. The building material between the wires will probably be of
awful dielectric quality anyway.

Just bring the pair of insulated wires close together for a short distance
and run them through a single somewhat larger hole lined with a short, pvc
or polythene tube. Slope the tube and the line to prevent rainwater from
running indoors.

When coming through glass or DRY varnished timber a single hole is fine. On
high power lines make sure the insulation on the wires where they are close
together is thick enough to withstand the high voltage at high SWR.

At HF, the discontinuity in Zo due to bringing the wires close together for
a few inches, even a foot or more, is absolutely negligeable. And there's
nothing wrong with changing from a long open-wire line (outdoors) to a short
ladder line to the transmitter (indoors).

Use a simple choke balun between the transmitter end of balanced lines and
the tuner. The luxury of a balanced tuner is unnecessary.
----
Reg, G4FGQ

====================================
Reg Edwards wrote:

Even a 300-ohm twin line with substantial conductors, not the flimsy old
TV
downlead type, will effect an improvement over the usual sort of coax.
450-ohm ladder line is most popular because of cheapness and relative
ease
of installation. But for perfectionists, on very long lines, a 5" or 6"
spaced 600-ohm work-of-art cannot be bettered.

any reason that silicon sealant would not be as good as anything else when
fixing (gluing) the wires to the slotted holes of the spacers in a
homebrew
ladder line? Any reason why this same substance would not be appropriate
to
seal up the ceramic tubes where such lines go through a wall?

this stuff is tough, weather resistant, sticks, and stays flexible.

Bill, K6TAJ