I had no obvious leak but I agree the filler tube can become porous over time. Last year I inadvertently tested this with salt water taffy. I had my 67 Mustang convertible at a car show at the beach. While there, we bought some salt water taffy (individually wrapped in wax paper, all in a big plastic bag). The trunk was pretty full of car show detailing stuff so when I threw the bag of candy in there it ended up sitting right next to the filler hose. Two days later when the show was over and we were home, I took the taffy out of the trunk. As my family and I started to eat it, everyone spit it out- it tasted like gasoline!
I have never smelled a fume in the trunk but obviously some were leaching out through the tube (probably as old as the car). I replaced it and used new clamps. Call this the taffy test!