You asked about the correct way to vent a tank. If your not showing the underside of your car at shows, why not install a late model evaporative system. You would need a carbon canister, vent valve or solenoid, hose to intake manifold vac. This would also eliminate an unpleasant raw fuel smell, have clean emissions (hydrocarbons escaping in the air) and has no effect on performance. Big brother wants to eliminate us rodders. If they see that we do what we can to "help" it may keep them off our backs.