I chickened out of the engine dropping malarkey.... I made an inspection hatch in the bottom of the wardrobe ( mines rhd ) to get access... then I could reach both ends to ensure the filler pipe was properly attached.
I would be checking the filler neck first. That was an issue on mine. To me if it was that lower one it would be doing it all the time. Stick your finger in through the filler. Should be able to feel any cracks on the bottom Piece 1
This was mine. The PO said it had a feint smell of petrol if they filled the tank, so they kept it below half full Every time you turned a corner, the fuel in the tank would slosh about and force vapour up the filler neck. Nice of the guy who painted the bus to take care about getting paint in the filler hole, too!