Did the dealer describe exactly what is leaking? There is a large clamp on the filler hose where it connects to the plastic tank fitting. Maybe the clamp needs to be tightened? Or does the filler hose need replacing? Or is the nipple fitting on the plastic tank leaking at the joint (from the wording in your post sounds like this is what is happening)? If you only fill the tank 2/3 of the way does the leak stop (no gas fumes)? Wonder if there is a PVC type glue like what is used on plastic plumbing pipe that can be applied to re-melt and seal the joint if that is where it is leaking, if it is just a small spot.
Here is a picture of the tank in 2010 Camaro:
This next photo shows the filler tube on right where it connects to the plastic gas tank. The whole Independent Rear Suspension cradle was removed giving a good view of the filler hose and clamp area.
Replacing the tank sure would not be a fun project if the car was not on a lift.
Photos are from a Superchevy project found here:
http://www.superchevy.com/how-to/pro...r-fuel-system/
Ron