if it were a constant problem it would be a tank leak toward the top where there's likely to be corrosion from sitting long periods with condensation happening above the gas level, but if ocassional, check the rubber connections between the outer fill fitting and the tank neck, both the actual filler and the vent tube .... when you gas up, stop the instant it kicks off instead of "rounding off" the pump $ or filling it to the max - if that prevents the smell, the vent tube is the likely culprit
Bill
