I'm sure covering is best, and because of that belief, in the 3 such hives
that I have made for a local children's museum, I made covers to be put on
when the museum was closed.  They were put on religiously for about a week,
and never again thereafter.  The lights are turned off after about 6 pm,
though.  I have seen no evidence that the bees really cared.  No absconding
so far.  Sometimes there are too many bees, other times too few.  Wintering
over is a chore, but I don't attribute any of those problems to the lack of
covers.
 
 
Guy F. Miller           "Start every day with a smile, and get it over with."
Charlottesville. VA                                     W.C. Fields