I have a strong petrol pong in the boot but there are no obvious pores in the top of the tank. In saying that, it is not unblemished a vapour will find a way through any mildly porous membrane.
In my case, I think it more likely to be the rubber gasket around the fuel gauge sender that is allowing the fumes out. Just need to find a supplier for a new one.
those gaskets are used by contemporary Italian cars like the Fiat 500. Ricambio springs to mind as a source