Skimmed thru the article, and didn't read the comments - so maybe I missed it somewhere - but I once read a story in an old issue of Popular Science (1940s or 5

Skimmed thru the article, and didn't read the comments - so maybe I missed it somewhere - but I once read a story in an old issue of Popular Science (1940s or 50s), probably "The Model Garage" (my favorite part of that era's magazine) - where the explanation given as to which side the filler was on seemed logical enough (perhaps for the time - but it still seems to hold on most vehicles today): The filler is always on the opposite side of where the exhaust pipe is routed. Granted, this doesn't help if you have dual tailpipes (though usually the pipe is y-split just before the output), or if you have dual straight-pipes (I don't believe any production vehicles have this as an option - it is usually an aftermarket performance mod). But ultimately - the explanation was with the filler opposite that of the exhaust pipe, you decrease the issue of the heat from the pipe, or leaks from the filler, becoming a dangerous combination. That said - now that I think about it (I guess I'll need to crawl back under), my Isuzu VehiCROSS has the exhaust running down the passenger side, and the filler is on that same side. However, the exhaust is routed out the left (driver) side - I'm not sure how the filler pipe and everything else fits in there. Knowing the VX, though - given its "odd-duck" and somewhat hand-built "custom" status in the car world (rumor has it that with so few built, an assembly line wasn't created for them, and they were all hand assembled; it's known that a ton of parts for them are the same between the VX and Rodeo/Trooper/Hombre) - there's a good chance the routing isn't "optimal" (I just had a custom heat shield made to fit between the exhaust and a connector for the TOD module - owners have had it melt and water intrude into the connector - burning it and sometimes the module out - and given that they aren't exactly easy to obtain...well, I wanted to protect it from that possibility).