The only time I drain gas completely from our 2000 is to store it for the winter after also changing the oil.
During summer, I keep my Honda in my basement leaviving gas in it, ready to go.
No fumes and I feel pretty confident that keeping it in a basement and in the AS is farly safe, but take it out when you plan to use the trailer and maybe leave door/windows open for a bit.
The reason I am confident is because there were a few times that I forgot to turn the gas cap on/off knob to on, and the generator started to choke. So Ithink there is somewhat decent seal from the gas cap.