Sending unit ground strap, and fuel filler question??

If I am not mistaken, the mat between the tank and the car is there to basically to protect both the tank and the underside of the car, as well as prevent any unwanted noise from the tank and the car rubbing together.. i used roofing felt as the mat in my Dart... I dont know for sure if its a bad thing to not have it in there, but its something I would put there