I've had my all-band-doublet up at 90 feet for over a year now with
ladder-line spacers cut from polycarbonate sheet. Works great, is
kinda pretty in the right light. The polycarbonate is supposed to be
relatively UV-resistant and it seems to be doing pretty good.

But I have a hankering to use wooden insulators next time I put an
antenna up.

The old ARRL handbooks always recommended boiling wooden feedline
spacers in paraffin wax for weatherproofing. I suppose the idea is
that it's water-repellent. Don't know how long this can be expected to
survive weather extremes (ice, heat). In my experiments in my garage,
the wax coating seems to pretty much rub right off with my fingernail,
so I'm not sure how much good it does where the feed wires or tie
wires abrades against it.

Shellac is another option I suppose, but shellac seems to me to be
something like the enamel coating on magnet wire, and having used this
in rooftop antennas in the past I was quite surprised that in the
summer it gets hot enough up there to burn off the enamel.

Spar varnish seems to be the ultimate in wood coatings for weather
resistance.

Any words of wisdom? Or is polycarbonate really the cat's meow?

Having fabricated antenna stuff out of both plexiglass and
polycarbonate over the years, I am very very impressed with
polycarbonate's workability. It does not craze or crack the way that
plexiglass does.

Tim N3QE