Steve
Here's what you want....first you want to set up the ability to vent the Fuel Cell then Block it in case of a Roll over situation. So we start with a Aero Cap inside of the Cobra Cap.... and this gives you a space between the Aero Cap and the Flip Cap which is what you need to mount the AN-6 fittings for the vent lines
Now you need to drill some holes to the atmosphere for the ventilation of the fuel cell.
When the Aero Cap is closed and the Cobra Cap is closed the air can come up into the space between the two caps and vent through the holes you drilled.
Now you see the AN-6 Nipples and 90*degree fittings for the fuel cell... one for each side of the tank, so when it's full you don't have any issue with venting from one side or the other.
This is the Passenger side vent .... and if you notice it has a check ball in it so you are protected of a Roll over on that vent line ... but the AN-6 fitting on the other side of the Fuel Cell does not have a check valve in it line...
Now you can see the under side of the Fuel Cap .... this shows the two AN-6 90* fitting coming out of the cap and the two vent hoses attached to the fitting and below the fitting you see the AN-6 Check Valves in line to stop the fuel from coming out.... Also remember the most important item in this photo is the Grounding of the Cap to the Frame of the Vehicle so you don't get any Static when Fueling...
Here's the other side of the Cobra Fuel cap showing the AN-6 Check Valve on the other vent line so no fuel can escape during a roll over or accident.
Again check out the Ground Straps.
Sorry for the long Post ...but there's no easy way to say it...