My push-in headliner I got a couple years ago, was sagging down and rubbing my head when I drove. (Wrong head getting rubbed
To fix the problem, I got a roll of 1/2" foam at a fabric store and used the fabric from the headliner in the car. A can of 3M spray adhesive, masking tape and a piece of 150 grit sandpaper.
Headliner in all it's glory: before.
I took out the HL and traced it onto the foam with a marker. Cut it out with scissors.
Next, I masked off the trim of the top, then roughed-up the inside of the targa top with the sandpaper. (To help the glue stick properly.)
I sprayed the adhesive on both the targa top and the backside of the foam. Let sit until it becomes tacky. Then, position it into the top and smooth out any bubbles and be sure to keep it centered.
The same goes for the fabric, too. I sprayed the foam and the backside of the fabric with adhesive. Spread it out the best I could (trying not to let it fold together and stick to itself.) 2 people would be very helpful during this part.
I trimmed some of the fabric with a razor knife and then tucked it underneath the trim of the roof panel with a thin, flat tool. (Make sure you cut the fabric a little larger than the foam to give you extra to tuck in.)
After smoothing out any bubbles and finshing the edges, in about 2 hours, here is the finished headliner.
Hope this helps someone out. Thanks, John.