I once had an old motor home with a P30 chassis. The load limit for it was only 2000 pounds. That includes passengers, fuel, water and cargo. After discovering this I did a little research and discovered this is typical for most Class A RVs of similar size (mine was 31 ft.)
Here's the math:
45 gallon fresh water tank, full: about 360 pounds.
50 gallon fuel tank, full: about 375 pounds
four adults at avg. 180 pounds: 720 pounds
Just those three items total 1455 pounds, leaving only 545 pounds left for food, luggage, recreational gear, etc., which in total could easily exceed this figure in total.
In contrast, my 35 FT 1990 Crown Super Coach II had a capacity of over 15,000 pounds, and that was before i stripped it of its several hundred pounds of seats. Some of this would be used up by the conversion itself of course, but I'm sure the load capacity left over after completing the conversion would far exceed the 2000 pound limit that my P30 motor home had.