Hi there
A while back I scored some material that is used in the construction of cold stores etc. I don't know the proper name for it but it is thin metal plate sandwiching some polysterene. Without going out to check I would say it was about 50mm thick.
I had plans to make a temperature controlled environment for fermentation with it but that's looking less likely now so maybe someone else can make good use of it. You can pay what I paid - nothing.
I can help transport it if required as it just about fits on the roof of the truck. Easier to shift with a trailer though if you have one.
Cheers
Mike