Here ... I see you've posted directly after it, so perhaps have seen it already.
Just a quick comment on a homemade Twinstock ... I use the thinnest ply divider possible to maximise heat transfer between them (and maximise the number if frames I can squeeze in on each side). I then use a sheet of thick plastic pinned along the top of the divider as a crown board. All that lies flat on the top of the frames ... followed by a thick block of Kingspan. I actually think Correx would be a good divider - easy to clean/replace, thin and pretty rigid - but tricky to fix my plastic to.
If I need to feed them I cut a small flap in the plastic and use a curry container upturned with fondant in it. All of this goes in a poly super with bubble wrap to take up the dead space. Then the Kingspan and roof.