Something is terribly wrong because a condition like that in a new car would have initiated a major recall. You must have a broken connection or a tube that has rusted through.
Carefully follow the tube and use all your senses as you go. Move it around. Use a flashlight.
Is there a strong odor in your trunk? Is this happening on hot days? C'mon, give more detail because all I know is what you report, which is; this is the second time the vent tube is leaking after a fill-up. - Dave