Depends on campsite from our experiences. Some places say max is for example 30 foot and when you get there you can back up your rv over hang (distance from rear bumper to tires) a lot and have no problem. Other places might have a tree or pole or some other obstacle that you can't back up much. Other places might say max length of 30 foot and that might be their smallest rv site in the park and most of their campsites can hold much longer. So the "fudge factor" depends on how made the "fudge".
If your making reservations for a vacation I would check out by a phone call to confirm. If your just dropping in too spend the night or so during off season, just change to a different site or park. Another way that might be of help is to look at the campsite with google maps in their "earth" mode. And maybe see a bunch of Rv's your size, so you know you will fit. Then there is always the exceptions, We like this one campground that has really large sites and Hardley used. Reason is the road going into camp ground has a sign just of main cutoff that says max length of 25 feet and no trailers. But when you get to the park their is a lot of room.