Scrub scrub scrub the back side of the hd/liner. Attach thin closed cell foam to the hd/liner and let it set up. Do not glue hd/liner directly to roof. 3M 90 will work find, allow it to set up 30 seconds or a minute before attaching foam or to roof.
Plan B: We also sometimes use a thin magnetic sheet 3X5 it's a lot less work. Glue hd/liner w/foam to the magnet, set the magnet in place it'll never come down on it's own, yet you can remove it quickly anytime. The gain? You can move it around to get the best position. With 3M once you stick it and spread it out you'll come up an inch or three short on one side, or front/back.
Pantera Miami