If I remember from my times with a Unimog, the Mercedes manual suggested loading up the towing vehicle up to maximum weight when hauling extreme loads. This is partly to maintain traction and to readdress the imbalance in Trailer versus Tractor and help prevent the trailer driving the tractor so to speak. Most probably over there as here agricultural tractors haul massive weights on public roads with a far higher ratio of imbalance, however they are usually limited to fairly slow speeds and of cause they are specifically designed for traction and haulage.