Keep in mind that the gas tank sweats. The water produced is trapped between the insulator and the tank. You need something that will absorb the water and keep the tank dry. I don't think the reproduction pads will do this.

Hear is a comparison picture of the original tank pad material and felt roofing paper. They are about the same thickness.

The original has grooves and the felt doesn't. The grooves could be there to help channel the water build up away from the tank and allow ventilation to help prevent rusting.