Re: O ring material
I'm not sure you mean neoprene....not really an o-ring material.
Looking in a Parker o-ring material guide, NBR (Acrylonitrile-butadiene) will work fine in that application. Since it's not going to be in contact with the fuel like in a tank seal I wouldn't get to worried about the specific compound. That seal is there more to keep water out of the tank. Some of the NBR compounds will tend to swell more than others when in contact with fuel, but this seal isn't really in contact with the fuel.
A couple of the NBR compounds they list as fuel resistant are
NF162-65 (fuel resistant, UL listed)
NF153-70 (fuel resistant, SAE 120R1 class II)
N1500-75 (low swell, UL listed, fuel applications)