Could anyone help me on what is the best spray/brush on sealer to use on my
vertical antenna resonator?

I have home brewed the 80m resonator for an elderly Hygain AV-18VS, but need
to weatherproof it.

Is clear polyurethane from the paint shop OK to use?

Is there another more suitable commercially available sealant?

I would appreciate any help or knowledge please.
John
VKKCE