> While mentioning sacks and canvas, and plastic, I should mention the need
> for bee passageways over top of the frames in winter...
 
While re-reading this after posting I remembered that I should add the
following caveat:
 
We have had bad luck using sacks under telescoping lids for wintering here
in Alberta.  They get damp and mouldy since they cannot get rid of the
moisture through the upper surface.  Plastic has no such drawback, since
it does not absorb water.
 
If sacks are allowed to breath on the top surface, they do work well.  I
have seen them as the only lids used on hives in wintering boxes that are
filled with wood shavings.  Assuming the outer wintering box is drafty
enough to let the moisture out, they do very very nicely.  We have used
them with no other lid in our wintering wraps with good success, since a
porous plastic bag with insulation goes on top and the outer wrap breathes
well.
 
Allen