I see two problems - (1) the nipple for the vent on the stock filler tube is right inside the neck and points up, so when you put the gas nozzle in, the end is way down inside and not near the vent tube at all. It's hard to tell how far down the tube your vent is and I sure don't know the standard length of a gas pump nozzle, but it's something you might consider. (2) I presume that you will extend the vent tube to go through the floor. If you end it there, explosive gas fumes will end up in the trunk
