I finally located where the strong gas smell is coming from.
It's located under the driver's side back seat, next to the the left fuel sender unit. There is a gas plastic conduit that terminates without any connection at all. Gas fumes are flowing from that opening when the engine is switched ON. When i obstructed the opening with my finger the smell goes away.
Does anyone have an idea of what the pipe is doing and if it's normal not to have anything attached to it?