Fill the tank up then
Check/replace the seal around the sending unit.
Check/replace the fill gasket on the tank.
Check/replace the rubber seal on the cap.
basically look for clean spots on the tank.
The one thing I am sure it is not, is the cap. I got a new one from DamnRaider here and it seals great. Before I got that though I did not realize I had lost my old cap and as I came up the 3 floors of the garage making 3 or 4 right hand U-turns I guess I splashed gas all over the garage. They did not let me park till I fixed that. But that was many months ago.
I do smell it in the car too, is that a clue to where it leaks or not?