I use a piece of vinyl - covering to the second frame in from each side and same distance from each end on the broad box - above the queen excluder - to keep the heat in in winter (from April on here) and in top box under the lid to stop burr comb being built.
Winter? Sunshine Coast?
Your bees must be bloody soft.
OK, silliness over - Tas is generally reckoned the coldest State in Aus (although winter in Hobart is far more comfortable than it is in Melbourne) but even so our Winters are still pretty warm compared with Europe/North America; our mean minimum in July is 4.6 degrees C, mean max temp is 11.7C, so hardly what you'd called cold really. We get maybe half a dozen light frosts each year down here close to sea level.
We had masonite inner covers initially but found they became soggy and mouldy, so we ditched them and went without, leaving a clear space from the tops of the frames to the migratory lid.
We had no problems with chilled brood through the winter, nor any difficulties with them building burr comb infill from the lid down to the frames, so in our climate, I'd question the need for the inner cover. Obviously a different story in North America/Europe and in freezing cold holes like Ballarat, Canberra, inland NSW/Qld, inland Tas etc - horses for courses I guess but until we see a reason, I don't think we'll be bothering fitting the inner covers for the time being.
