In my case, I saw traces of leakage on the side of the gas tank, and the gas smell occurred the most often and strongest right after a fill up. So that's where I looked.

If that's not where you're finding your leak, I would suggest looking along the fuel lines. Does you engine use fuel injection? There would be two sets of lines, the pressurized source line, and the return line that bypasses excess fuel back into the tank. A potential leak is in the pressure regulator. There is a vacuum line that attaches to its top side; you can pull it to see if there is fuel in there. That indicates the regulator is leaking, and needs to be replaced. The other thing that can cause gas smell is the fuel vapor recovery canister; its line has been known to break. But most of these problems can cause the engine to run badly.