You can't reserve camping online. That can only be done in person. Read the instructions on the camping page of this site. Even if you cant be here when the gates open on the 4th, there is always room to park when you do get up here.
If you want to come the weekend before and save a spot you need to have a tarp that you can stake in with your name and address clearly written on the tarp. You also need to have tickets.