This shows the vent line on the outside of the car so you can see where it goes when it's installed from inside the trunk....the gas has to climb a long slope before it can spill over & down on the ground
Summary is three things: gas cap upgrade, install plate with a flapper inside filler tube, & improve existing gas tank vent line...........have fun...Don
You will also find that gas is dumping on the ground thru the vapor/vent tube that is inside the trunk attached to the filler tube & running down thru the trunk. I'm installing a different vent line that runs all the way up into the roof & back down to stop that from happening...I'll get a picture & put it in my picture area so you can see the method....Don