It looks like the vent is the source. I have had a hose on the vent for a couple of days and no more smell at the engine bay window, but definitely a smell at the end of the hose. I don't have a fuel on the end of the hose yet.
When the tank was out, I filled it with water and checked for leaks. However, it's no guarantee that the tank does not have a pin hole or crack somewhere. It only has about three gallons of gas in it at the moment.