O.K., as I understand it then, you have the neutral grounded only at the generators/power distribution unit, and the ground bar on the new panel is grounded just to the local rods.
I know this wouldn't be to code by the NEC, but this is generally accepted practice in Europe, though you must use a main GFI because the loop impedance will be too high to clear a ground fault with a normal OCPD.
If the new panel is metal clad, then the GFI would have to be either at the genny end of the feeder, or fitted in a fully-insulated enclosure in front of the new panel.
