I live near Ottawa, Canada.  Brief climate summary: Temperatures are often
down to -30C in the winter, and as high as +30C in the summer (except for
the current heat wave where +35 seems more typical.)  There is snow on the
ground perhaps 5 months of the year, and the winter air is quite dry.  In
the summer it is often very, very humid.

I am beginning to invest in larger numbers of hives now and want to paint
them with the most durable protectant available.  I don't know what that is.

My first hives I painted with deck sealer.  I reasoned that wooden decks,
being horizontal, must survive standing water and intense sunlight.  That is
worse than what my hives will experience.

The result was a very attractive natural wood colour that I quite like, but
recently I noted in the directions for the deck sealer that to repaint, I
must first remove all traces of the original coat.  Oh dear - that could be
quite a chore!

So I am re-evaluating what I paint my hives with.  I believe that oil based
paints last longer than latex based paints.  Will marine enamel last longer
yet?  Should I apply a sealant of some sort before  applying the paint?

What is the most durable, most effective thing to use?

Frank.
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The very act of seeking sets something in motion to meet us;
something in the universe, or in the unconscious responds as if
to an invitation.  - Jean Shinoda Bolen