Letchworth State Park in NYS is the only park we've had that issue, and not at the campground, coming into the park to get to the campground. If we were going to drive the RV around the park as well as the car, sure, charge me. But when the rv is going to sit on the site same as a trailer, then they shouldn't charge.
Also, their rules state you must pay for a second vehicle, so they are considering the rv a vehicle. Their rules also state you are not allowed sleep in your vehicle, so we technically aren't allowed sleep in our rv while there, since they decided it's a vehicle.