My 95 SC400 smells like gas inside. Smell comes thru the vents. on 1995 Lexus SC400

It also smell very bad when you step outside the car. I just had the car at the dealer on friday. They could not duplicate the issue. The car does not smell all the time. I had it out all day today and I did not smell gas until I was on my way home. It was about a 35-40 min ride on the highway. When I got off and stopped at the light the car filled with the smell of gas. What could be causing this if the dealer check the fuel system and could not find anything?

Asked by for the 1995 Lexus SC400
Bad Catalytic Converters do this. Do it.