I use 2 inch foam board in an empty box above with a hole drilled though
the center.  Allows venting of moisture and generally prevents condensation
on the foam.  Thus far the bees haven't chewed the pink foam and it allows
me to pull the foam up to place a sugar brick below without exposing the
bees as much... Though if you slack pulling it out they build a nice nest
of burr comb in there... I would put it above the inner cover but that's
not good for feeding and moot if you're using migratory covers.

Jeremy
West Michigan

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