It's a good bet that the sending unit cork gasket is at fault, because there is really nothing besides that little round cover-plate separating the sender from the hole thru the floor for the sending unit. So, you'd definitely get the smell.
Another thing to check is the rubber hoses that connect the filler neck and vent tube to the tank. If your gas tank is overfull, gas may be encroaching upon those hose connections. If the worm-gear clamps are not tight enough, some gas might leak, but I don't think you'd smell it so much inside the car.