Is this you first twin carbed, air cooled engined car?
These cars tend to have a certain smell when parked in the garage after a run. I personally love it. Part gas part oil on a hot air cooled motor.
The fuel bowl in the carbs are also open to the atmosphere, so your going to get a tinge of fuel smell, even when it's cooled off.
If you've checked everywhere for any unusual leaking or seeping, I'd say your good. I'd check around the carbs and inspect the fuel line and fuel filters back as far as you can. Also look under the front of the car to see if there is a leak there from the line going into the tank. This is where your fuel pump might reside too. These are hand made cars and take a certain amount of sorting after receiving it. Your carbs could also being running super rich.
My not so mechanical brother in-law was visiting from that side of the country. He ran into the house alarmed that he smelled gas in the garage. I just laughed at him and told him that's the smell of performance. That, and there are 3 chainsaws, a weed wacker, and generator sitting next to a car with twin carbs. Your going to get the sweet smell of gasoline.
If, after a thorough inspection, with no leaks, you can't stand the smell, then maybe letting it cool off with the engine lid open and the garage door open might be what's called for.
Good luck.