There's a 'roll-over' valve where it feeds into the fill tube that prevents leaking.
I did have some dripping once, I think because of bouncing down the road. Because of that, and for convenience, I have bought a solenoid actuated valve that I can operate from the cab. I'll be able to shut the flow down when near full.
One thing that I have had happen is the fuel guage drops to zero sometimes when moving and filling, I guess because the computer can't figure out why fuel is being consumed but the level isn't changing and rather than show a false positive it drops to empty.
The next cycle of the key resets it and all is OK.