Tailight housing bolts and ground question

[BrianG]

I am getting ready to put my taillight and reverse light housings back in and was wondering how they ground. After reading several old posts on this board, it appears as though I should either/or both clean the back side of the housing where it will touch the bed and I guess I'd also have to remove the paint from the bed in that same location. Or, I could run separate ground wires which I suppose wouldn't be all that hard to do.

What I don't understand though, is why do the bolts that mount these housings have rubber washers? Does it provide some sort of dampening that is supposed to help the taillight bulbs last longer or something? It seems that an ideal way to ground the housings would be through the mounting bolts using a good star washer. Just wondered if anyone had any thoughts on if the rubber washers were really needed and if anyone had any other tips or recommendations for grounding the taillight housings.