Thanks to Chevynut for putting me in contact with his interior guy. To recap, I was pretty happy with how my headliner install looked, except for the rear corners. Try as I might, I couldn't get those wrinkles out:
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After the interior guy looked at my pics, he gave me a few tips:
* In attaching the rear of the headliner to the rear tack strip, not only pull toward the window, but also pull toward the corners.
* With my vinyl headliner, use heat on each wrinkled panel, starting from the front most wrinkled panel and working toward the rear. The heat makes the vinyl headliner more supple, and able to be more easily stretched.
Those tips were key! Having read plenty of advice to be careful in using a heat gun for fear of quickly blowing thru the headliner fabric, I had been too timid with the heat. I had a small piece of fabric that I had trimmed from the front, so I experimented with the heat gun on that piece to get an understanding about what the fabric could take. I also used a fine marker to draw a circle on the piece to see what stretching I could get. It could take quite a bit of heat, and would take quite a bit of heat to stretch the fabric. I didn't go crazy with the gun, but did heat it quite a bit more than I had previously. I also had to trim some of the listing pockets a tad more, because I was stretching more.
After using the interior guy's tips, this is how the corners turned out:
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