The generator prep in our Landmark included the sheet metal enclosure, the wiring (3#6 & ground) to a j-box outside the generator compartment (which also had two 30 amp 'push to reset' breakers, the transfer switch and the remote panel (Start, Stop, Prime and hour meter) inside the coach.
I installed my own lightly used 6500 watt gasoline Onan. I would have loved to get my hands on a low hour Onan diesel. I looked at several on ebay and had my doubts that I could get them to fit in the front compartment. If I ever get the chance and the price is right, I would take a stab at shoehorning it in.
John