We average about $550 per month when not moving for campsite and utilities. We've been wintering in Florida since November. Last year when we we were in travel mode, it averaged more like $900 per month. Diesel fluctuates depending on how much we towed the rig, but could easily be $500 per week in high mileage weeks. All your other expenses (Food, cell, gasoline, entertainment) will be to your lifestyle and pretty much MORE than you spent at your s&b. We find ourselves paying more fees for sightseeing, activities, etc. than we did at home, though we went out for dinner more so it may average out. Annual insurance on the rig is about what our homeowners insurance was, so you don't save there either. Of course we're not paying property tax, so come out a little ahead on that.
Our idea of full-timing is traveling and seeing the sights in each state, so it is more expensive than being stationary. YMMV.