Hi Dave. I am equally baffled by the source of the smell - it just went away! However, when driving in town with the hood up and the passenger window open a little, the smell returns. I think it may be coming from the area of the filler cap itself and at low speed, the low pressure area created behind the back edges of the hood cause the smell to be sucked forward! Hope that makes sense.
Also on my car, the fuel tank filler neck doesn't appear to be connected to the car body. I think that there should be some sort of seal around neck to prevent spillages entering the car - because of this I am always very careful when refuelling the car to prevent any spillages. It is frustrating and I am open to further suggestions! Steve