Gas leaking from middle stern below drain plug

[SkunkBoat]

Assuming you have a belly tank?

The tank compartment is a "dry" compartment. It doesn't drain to the bilge.
The fuel would really have to be filling up the foam and leaking over the top of the tank.. I would definetely check all connections as the others said, Check the gasket on the sending unit....filling up and tilting the boat can cause it to seep.. Definitely remove the hatch cover and inspect.