I have this problem and I have not been able to resolve it.
See this thread..
http://986forum.com/forums/general-discussions/57332-p0455-car-smells-like-gas.html
P0455 Fuel Tank Ventilation System (Major Leak) - Below Lower Limit Potential causes: - Tank cap missing or O-ring bad or missing. - Ventilation lines detached from EVAP canister. -
Ventilation line detached from tank. - Ventilation lines detached from operating vent valve. - Ventilation line detached from fuel tank vent valve. - Break in ventilation lines.
I haven't been able to dig deeper because i'm not sure exactly where the bolds above are located. Does your car smell like fuel? Mine does a little bit, i'm sure I have a leak somewhere, but not sure where.