Even though no codes are appearing, chances are, a code will set in the future. Two years ago I had an evap code that drove me nuts. I constructed a smoke machine and found no leaks coming from any lines or components of the evap system.
Changed the gas cap for a new one. Still getting the code. I started putting the gas cap really tight. That's when the evap codes went away and never came back. The top part of the fuel filler neck that contacts the rubber gasket of the gas cap had
no rust or corrosion. I figured that the top of the filler neck had fine scratches and allowing the cap not to seal. So, whenever I fuel up I make sure I muscle the gas cap on good. This is on a 97 Buick Regal.
You could have that same issue. Try tightning the gas cap real tight and see what happens.