[A1971Blazer]

my friend and next door neighbor has an upholstery shop and does interiors for higher end restoration vehicles...
For a lot of panels, he uses a PVC sheet that is used in boat interiors. It can be heated and molded, glues strong like PVC pipe and is impervious to moisture.
For some panels he uses a tool I made him to recess small magnets (1/2" round x 1/8" thick) flush into the sheet then glues them in place. As far as I know, he's never had an issue with them coming loose.

He will be doing my '67 interior when the time comes. I plan to make my own trim that will attach to the headliner and the entire assembly will be held in place with the magnets...