Help with grounding a generator on a running vehicle
Note this answer is from a 230V european perspective. Our electrical wiring uses three conductors: L=live (230V), N=neutral (return wire), E=earth

With a running vehicle you cannot "ground" the electrical system. Also: very likely, you are not required to ground any generator installed in a vehicle according to your own national regulations. Such power supplies are typically excluded from the grounding requirement. (Check this!)

Nevertheless, your electrical installation will need proper earth conductor wiring to ensure circuit breakers work properly in case you have a fault somewhere. Since this conductor has no connection to the "soil" (for lack of a better word), you will need to "bond" it to ensure a return path to the gen set.

Generators typically have two wires: the voltage 230V occurs between the two leads. Intrinsically, there is however no "earth" or "neutral" wire.

To connect a generator to a 3-wire electrical installation, one chooses one (any one) of the two wires exiting the generator as the "live wire" and the other as the "neutral wire". In addition, one "bonds" (i.e. connects very permanently with thick wire/bar) the "ground wire" of the local network directly at the generator to the "neural wire". This ground network should also be bonded to the chassis/frame of the vehicle and the frame of the generator.

Note: it is highly advisable to install a RCD directly after the generator exit (before any circuit breakers but after the neutral-earth bonding).