Wow ! Thanks for that @Cowgirl
I will look into that. I was already planning to do honeycomb in medium supers. That would definitely save a lot of trouble in cutting out frames and packaging.
XPS board installed as a barrier at the bottom part of the cover is quite popular choice these days. Check what thickness actually fits there.
We also need to take into account that after the roof insulation, the next affected part will be box walls. At the moment your roof works as a condenser, where vapour cools down and sets in form of dew. After roof insulation walls will pick up this role. But, at least, it is not going to drip from the top on bees.
With XPS installed, under-roof space will become a separate compartment less exposed to vapor from the hive below. Ventilation holes in gables should help with extra moisture in roof timber. Mesh on those holes would be beneficial to keep away fauna you are not planning to keep 
The question, is it really worth it to make the cover completely air-tight? Like one of those setups @Doug1 showed, where top of box was covered with thick film. Or leave a minimal opening to let some moisture to escape (though, with some warm air). On one hand some people argue that in nature bees donât have an additional ventilation holes in natural nest sites. On the other, current hives with 20 mm walls are not even close to tree hollows. In Shulgan-Tash Nature Reserve they work on creating natural nest sites for Russian bees by hollowing trees and logs since 1958. They found that bees prefer hollows where they have 200-300 mm of wood around the nest. At such thickness wood itself actively contribute to humidity regulation in the nest. Wood absorbs moisture when humidity is excessive and gives it back when it is low. So, direct application of natural tree hollow ventilation principles to rather âartificialâ hive could be less than ideal. I guess, it gives you an opportunity for an experiment to find what works best in your conditions: to vent or not to vent? 
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Gâday Tony, were you, or anyone else, still interested in the Hogg Halfcomb Cassette system? I have an arrangement with Herman, the manufacturer in the USA to be his distributor in Australia but Iâm trying to drum up enough interest from enough people to buy a pallet load from him.
I still have a handful available, these are complete Hogg Halfcomb Cassette Superpacks with custom supers and followers made by me here in WA.
Look me up on Facebook at West Coast Beekeeping Supplies for more info. Thanks,
Regards,
Thommo.
Hey Thommo,
Just a note to readers that these wonât work in their Flow supers (though could be useful for Flow Hive users that have a second super or also use other styles of hives).
Gâday Freebee2 and all readers, sorry if I was not clear in my last reply, the Hogg Halfcomb Cassette system is an independent system to the Flow Hive, requiring a new super. It is designed solely for combed honey. It must be run above the brood box and queen excluder, with or without a Flow super above or below it. It is additional to, and can compliment, rather than replace, the Flow system, thanks,
Regards,
Thommo.
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Hi Thommo,
Thanks for clarifying this info for our readers
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