It is much more likely to be a site management issue than just plain greed. The last thing most parks want is someone pulling in with an RV towing a car and 4 other people driving their cars joining them. I have seen very few RV parks that have room for more than one or at the most two, vehicles besides the camping unit at the site. I would think they would even attach the fee to those off road vehicles if they had someone pull in with an enclosed hauler and then proceed to unload a half dozen and start parking them all over. If they are kept on the trailer or in the rear of the toy hauler and removed only when in use and then returned to that space, I doubt most RV parks would know or care. But private parks surely have the right to charge whatever fees they want and government entities can also make any rule they choose. No one is forced to stay in a place where they feel the charges and policies are unfair.