Ok cool, I was thinking that maybe thats how the guy showed me in the shop, with that board on last. I reckon if I do that and fill it with insulwool it would be a good idea.
I watched some vids from germany I think and they were covering the frames with a plastic sheet then the lid. I dont think this would be a good idea for Aussie conditions tho, too hot.
My conditions are more like the Med. than anywhere else in europe they say. Nothing in the Uk comes close, as for the US, probably the southern states come close.