[MikeMoller]

I know of a few stock/super stock cars that have used adhesive backed felt squares applied directly to the roof metal. Somewhat tedious to do but those cars have always passed tech. You can get them at 'Michael's' craft shops, peel and stick, hold up well, couple of color choices.

I have also seen regular headliner material ( couple of fabric places in town here carry that material.) glued right to the roof metal using 3m spray adhesive.