I agree. Don't bother with the onboard generator. Those Onans are loud, heavy, and cantankerous. You will never run it because you won't be able to stand the constant droning in the camper!
That opens up some options for you. Not having to have a generator means you can drop down to a lighter camper, which means you won't need a dually.
IIRC, skipro3 is overloaded by 3000lbs on his truck. He's hauling around 3.5X the manufacturer's recommended payload for his truck. While he is happy and it works for him, there is no guarantee that you will be happy or it will work for you. You can roll the dice and possibly end up with a $75,000 rig that you absolutely LOATHE, but I would recommend trying to aim for closer to the manufacturer's numbers.