OCCC varies by make/model/options - which is why there isn't much info on that out there. It's mostly trial and error.
Lichtsinn RV sometimes lists the approximate OCCC of some of their inventory units, but it depends on what's on it, and what's not.
The Onan QD3200 is only about 30 lbs heavier then the QG3600 model, iirc.
Winnebago seems to have (generally) decent OCCC numbers on their stuff, like the View/Navion, and/or Vita/Porto, but real OCCC has to be determined by actually weighing the finished unit, with the diesel/DEF/propane/fresh water tanks full, and the engine/rad and whatever else full and ready to travel. Then weigh it, and subtract that from 11,030 lbs GVWR, and whatever is left is your OCCC for that unit.