I owned a RV Park (small) outside of Mojave, California. I never heard of charging visitors. Of Course we would count heads in the RV when they arrived and charge accordingly. Our biggest pain in the back side were the Clubs like the 'Coast to Coasters ' who wanted a substantial break on the overnight. My manager explained we were a private Park, not Walmart!
If Visitors were to stay over night , they would be charged.