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