You can check with a company who used to build gas tanks for some of the trailer manufactures.
Transferflow.comThere are a lot of recent regulations (since 2004) that limit the fuel evaporation from fuel tanks. Before 2002, allowing 1 ounce of fuel evaporation per 24 hours was acceptable, however by 2005 Ford had to change their fuel system to meet a less than 10 grams per 24 hour fuel vapor loss. There are 28 grams in 1 ounce. So they can not even have a fuel vapor recovery tank, as it can allow some vapors out of the tank when it is warm out.
Fred.
