We put our fuel tank in place and marked the general location at which the filler neck will be. We then removed the gas tank and drilled small reference holes from the bottom. We placed the new gasket on the top side of the floor, centered it over the drilled reference holes, traced the gasket, and cut the necessary opening. Remember to cut the opening smaller than the gasket so it can be attached to the floor when you're done. Reattach the fuel tank, and slide the filler neck through the gasket and into the tank.