<< Will polyurethane finishes/stains work for beehives? >>
 
Polyurethane finishes/stains are fine if you want a nice looking hive.
 Definitely use spar varnish or some other type of exterior poly.  However,
the poly will not last and will continually need to be recoated.  I use
linseed oil as it is easier to put on (lazy me) and also preserves the wood
just fine, although it darkens it considerably.  I try not to use poly
outside because of the maintenance involved.