[OG68]

Hmm. The thin vinyl woodgrain is the only one I'm aware of and it, as you said, requires the backer.
Our sponsor sells the backer and yes it's $100 and you do need it. Without it, the pebbly dash surface shows through the vinyl.
The factory used a thin plastic backer which usually stays with the original vinyl overlay when you remove it.

The aluminum backer is flat and needs to be contoured before final installation. If it isn't contoured, it will peel away from bezel near the center. I gently bent it to the dash curve using old ball bearings and rolled it back and forth.
The vinyl isn't easy to apply either. It can stretch and become deformed. Relief cuts may be necessary to make it fit around the gauge openings and switch cutouts. There will be some space between the gauge openings and the vinyl. The factory vinyl wasn't perfect either.
Trimming may be necessary around the radio.

This requires a great deal of patience to apply correctly and on the bench. It can be done in the car but...