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

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics