You need to consult an electrician. You need to wire it for 120/240. You can’t just wire it for 120 (unsafe). Bond neutral and ground and you MUST use grounding rod at the generator/trailer. 2 hots, 1 neutral and 1 ground to box. The unit can operate in single or three phase. You need to make sure settings are all set to single phase 120/240.
Again, consult electrician.