Every model is different in layout and design. We RV'ers seem to have varying taste, tell me it ain't so. My unit has the fresh tank over the axles and 3 waste tanks in front of the axles. So I figure carrying dirty water must add to the pin weight. Now the basement seems to be mis-named, more like a split level but all the treasures that I must have also add to the pin weight. I put a bunch of necessities in the bed of the truck, guess what it doesn't add to the pin weight but it still goes on the rear tires of the truck.
I always try to plan for the worst, GVWR x .25 for added weight to my trucks rear tire capacity. This method has worked well in the past so I will continue to use it until something better comes along.