I'm going to give
this product a try.
It's a Marine fuel/air separator. It is designed to allow boat tanks to be filled without gasoline coming out of the vent. It also works with fuel agitation due to waves and such. If there is still a smell, then you can add the charcoal canister (btw, anybody got a source or pn for one?) to the output of the fuel/air separator.
Cost is about $80.
jp