When we were researching the purchase of our rig (11 years ago), I estimated we'd need between 2,000 - 2,500 lbs. for people, water, food & stuff. The rig we settled on had an unloaded weight of about 18,800 lbs. (including full fuels) on a 22,000 lb. GVWR chassis. Various trips across the scales have put our travelling weight from 20,600 to 21,500 pounds which implies anywhere from 1,800 to 2,700 lbs. of people & stuff. We do not full-time, but have travelled for a couple months at a time.
We have travelled with 5 - 8 people, depending upon the trip. The time we had 2,700 lbs. of cargo was the one time we travelled with 4 adults instead of the usual 2.
~Rick