Just thinking, if in addition to a rubber etc gasket, to stop your board getting busted or damaged from truck mounting, you also had a rubber isolated bolt/screw, then the truck would truly be rubber isolated.
Might be as effective at rumble elimination as pneumies. I would think it would require large head, to better contain a thick rubber washer.
This with even the standard 1/8 inch or better yet, 1/4 inch shock pad and you have plush. I THINK.