I have been going through this for over a year. I had it up on lifts in the spring and inspected by myself and other mechanics. Reached all over the top of the tank and couldn't find ANY dampness or fuel residue. No evap codes. Really irritating.
This fall it got really bad. I had visitors to my house mentioning the smell, I had people calling my work because they smelled gas near the truck. I climbed up under the back with a shop light and my cell phone and finally got a snapshot of the sending unit and surrounding area that is soaked. So either I have a bad hose connection, leaking o-ring seal, or it is rusted and leaking through. I am fairly rust free for a PA truck as well.
Still in my planning phase of how I am going to move forward in resolving this. Still in the investigative phase. A scope would be really handy right now.