TPB,
You might already have a technique for locating where to make holes in the cardboard, by making a template or other measurements. Here is a technique that works well with both the interior sunvisors or door armrests (if you do not have a template):
Obtain six 1" screws that fit the sun visor holes in the roof. Cut the tops off the screws, ground a rounded point on the top of each screw, and cut (with a Dremel Tool) a slot in the top of each screw (a screw driver slot).
Then, screw them into the mounting holes, allowing them to sit "proud" (outwards) for about 1/4". The headliner is then dry-fitted into place and pressed against the screw heads. After removing the headliner, it is an easy matter of drilling the three holes on each side and placing a larger hole between the screw holes. This technique has worked fine for me (and, I have gotten three uses out of that set of "fitting" screws).
Tim
