I found it depends on how much is hanging, how long it has been hanging and how much it has shrunk.
I tried 3M's Super 77 spray on adhesive as suggested by someone in some spots and it worked, but not in others. I understand Super 90 is stronger, I now see they make a FoamFast 74
that is meant for gluing foam. Wish I had tried it.
For those spots that would not hold with the Super 77, like the rear 1/2 of the ceiling that had been hanging for 10 or more years, I used PL Premium with a fine notched trowel.
In all cases, I found it beneficial to hold the Ensolite in place using memory foam and a peice of plywood so the lining would conform to the body curves while the glue set.
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