We charge often at campgrounds. We generally ask and there have been no issues. We haven’t been charged yet but that’s probably because we just rent 30 amp sites. I know some campgrounds have user pay fees for charging on 50 amp sites and others actually have pay as you go charging equipment on site. KOA does this.
But for us on 30 amp sites we generally either plug in the trailer or the car but not at the same time so it’s really no extra cost for the campground operator.
Funny. In the campground we are in right now there is a line of Teslas and other EVs in the staff parking lot. The owner and his wife both drive Teslas. 1 out of 5 vehicles sold here is electric and that will apparently be 1 out of 4 by years end. Teslas are more common than corollas here.

.
Here is a pic of us charging on a 30 amp site.