The headliner in one of my El-Caminos used to inflate like an air bag at highway speeds with the windows down,eventually it would block your vision,and became a hazard..I tried using 3M super spray adhesive by shoving the straw nozzle thru one of the holes in the fabric and spraying it on the roof,then pushed the liner against it and then away,and let it tack up...it held great for a few months till summer heat made it fail again...
One day while dumping my trash at the dump,I was looking in the metal pile to scrounge for anything worth hauling home,and I saw a large set of venecian blinds made of metal someone scrapped,that had to be 5 feet across at least,they were scattered all over the ground....a light went off in my head,and I scooped up all the ones that weren't bent up,took them home,spray painted them silver,and shoved them into the plastim trim around the doors and across the ceiling,which put an end to my sagging headliner blues,and it actually looked good too!...