The porblem is hidden behind the left side of backseat. Fold down the back side of the seat, open the cardboard that sits on the left wall. for opening you have to take out the bracket that holds the back seat take.
Inspect the fuel filler pipe as it gets rusted as water damages it from the inside of wheel arch. I had the same issue, which was given me fuel smell inside car, the same pipe is also culprit for the fuel back return while filling the fuel at petrol pumps, whenever i pumped air out of charcoal canister it give water almost half cup water. basically it was taking water during washes and rains.
Cardboard behind the back seat
bracket:
inspect the full filler pipe:
