I have been researching it as the core in place of foam between plywood skins. Not sure if that is what you had in mind. Thermacork seems to be the supplier for several dealer/distributors.
Great work on that lining! I might try to emulate your method(s), to both insulate and refine my TTT's crude interior (but, it goes so well with the crude exterior!), and give the interior a bulwark against condensation. I never considered insulation until well past a convenient stage to install it, and my later attempt to use a denim/mylar insulation just didn't work. I may not even need the foam board, but just the foam-backed headliner material may be enough for my needs in Texas.
About headliner application methods: I've used headliner-specific glues to install a couple (OEM-resto headliners for two of my old Chevy projects, '66 Chevelle & '69 C-10), but I also used 3M Super-77 on two other headliners (my wife's old '85 Lebaron, and my late/lamented '86 S-10 extended cab). I don't have the three last-mentioned vehicles to see if the headliners are still glued on, but the Chevelle' headliner is still OK, after 23 years). The OEM glue holds well, but is inconvenient to use, so I think I'll use Super-77 if ever I start the next headliner project. It was also my choice for use at my job, for many years, for applying identifying labels/barcodes on letter-sized paper tags to attach to plastic wrapping on palletized newspaper products. We used up cases of the stuff, even using a bare spritz of it. The tags would hold fast, even for months, when I had to store the pallets in un-climatized areas of my warehouse. I trust it, very much, though I just recently got a spray can of Gorilla Spray Adhesive, which I want to try on an outdoor project. It's cheaper than Super-77, so I don't expect as much from it as from my old stand-by, but I'll give it a shot (I'm a real fan of Gorilla tape, and this'll be my first try of their other products).