As I look around at my neighbors in RV parks it seems not having a pet is the minority situation. So if business is good some park owners have decided to gouge their guests. That's how I see it.
Motels, a different story. A five or even ten dollar fee is reasonable, at least for my shedding mutts. But I fail to see a justification for a fee in RV parks. A dog run is used far more than a pool in the vast majority of parks, and insurance for everything is a fact of life, given our enormous numbers of unneeded law schools, soon to outnumber law school applicants. Thank the Lord medical schools still require their graduates to be able to read their exams. :B
BYW, we're yet to be asked to pay a pet fee.