Thanks, Steve. So if I understand you correctly, your main concern is that the standard flapper valve doesn't work quite as well as a NASCAR ball system (or the newer Fuel Safe flapper that's designed for remote fill, I guess). I understand the concern about fuel in the filler neck as well - it's outside the cell and it's unconstrained if the neck is torn off. However, that's a problem with any remote fill setup, regardless of what kind of check system you have. Even the NASCAR system with the balls and a positive closing vent will spill any gas that's in the filler neck, if it's ripped off.

I guess the answer is to run a series where you don't ever have to fill the cell completely full.