19 foot 2003 polar center console

[steplift20]

My son has that boat and the problem is first the fuel fill is in the stern and the vent is on the port side by the stern,when he fills it up with gas and parks his boat in his driveway he keeps the bow higher then the stern, when it's hot out the fuel tank expands and pushes the deck up and cracked the access plate It's not venting, the vent and line are new When he opens the fuel cap all the are comes out So why is she not venting? I would like yo know and do would he Thanks for any help in this Mather