Easy fix. Like others have already stated you need to build some elevation into the vent hose to prevent the fumes. Think of the way a sink trap works (in reverse) with standing water in the J-Tube to prevent the sewer gas smell from backing up into your house.

Just connect the vent hose to a piece of 5/16" steel flared tubing. Run the tubing up through the trunk floor or behind the rear seat. Run it all the way up to the highest point and bend a 180 (u-turn) in it, and then back down through the floor again. I then took a 1/8" NPT Ford type carb fuel filter and screwed it into the boxed frame and a short piece of hose connecting it to the new vent tube. The gas tank is vented to atmosphere through the frame "outside of the body" but running the tube through the body allows the height needed to prevent the fumes. Just make sure you size the vent tubing based on your estimated fuel consumption. It works!