Ask when you reserve. See if it’s possible, whether it’s free or not - the answers will vary according to the campsite. Some are afraid that guests will rent accommodation for four people when there are six of them, and do not accept tents on rental accommodation areas. Others will ask you to pay an extra charge. Lastly, some will not ask for any extra payment.
With the children who want to play at Cowboys and Indians during the holiday or your teenager who wants to be (relatively) independent, you may want to set up a tent near your mobile home.