Edit: purely for realism and immersion of course.
There is no reason for fuel trucks. Unless I run outa fuel in my plane and I land on the ground and a squady comes driving me fuel for my plane because a lot of times that has happend to me. This way I will be able to get a successful landing and put my kills on the board lol.
GVs dont travel anywhere. They spawn close to their destinations and just maneuver a little around it. Why should they run out of fuel from such a short drive?
GV's should run out of fuel. Gasoline trucks would bring out more fuel. When the fuel tanks are down at a field the gasoline trucks are disabled. It would add another strategy to the game.