Newports have a GVWR of 18,000, so 20-22% would be 3600-3900 lb. To be honest, if you're going to load it up to near its maximum weight, it'll probably be over 4,000 lb. on the pin. We had a Big Country 3950FB, which is the same floorplan. It had a gross of 16,000 and we were running very close to 4,000 lb. on the pin when we had it loaded to 16k.
We full-time and you'd be surprised how quickly you can pack 3,000 lb. of stuff in a fifth wheel.