>Can someone explain to me what the advantages are of the tin-roofed,
>telescoping hive cover over the simpler (and far cheaper) "travel" cover?
>I can see that the sides of the travel cover...
 
As one who has used both, I'll have to say that both are good, as is a
simple flat piece of plywood.  Nonetheless, after years of experimenting,
we have settled on a telescoping lid (with or without metal) and a plastic
bag of kodel insulation as an inner cover, even though we still own 1000
or so of the migratory style and use them in a pinch.
 
We are migratory, but find that mass, not volume is the limiting factor in
transporting hives the way we do it.  Pictures at 11.  The space between
hives required by the side overhang makes handling much more pleasant, and
the overhang reduces the amount of water that gets into the hive.  Water
running down the outside will often 'wick' through cracks.  We had this
happening under lids and it resulted in water in frame feeders and water
on standing floors if they happened to be at all tipped back.
 
Contrary to what one might think, the telescoping lids blow off much more
frequently than the migratory type, even with an eight pound brick on top.
 The reason for this is that around here it is little twisters (dust
devils) that are primary lid lifters and the rim contains vacuum.
 
Nonetheless, we like the wind barrier that the overhang provides and the
drier interior that results from conveying water farther down the side.
Moreover, with sacks or pillows, the lid provides protection from sun.
 
If you want to put patties on top of the frames, a telescoping lid will
allow a sheet of plastic to be used above them to keep draughts out, since
all sides will be folded and held down and an reasonably good seal can be
achieved.
 
Allen