Here’s how I would do it.
Go to
www.Wanderinglabs.com. Join the site. Add a Request for Bahia Honda SP. put in the details for what you want and wait. When you get a notice of a cancellation drop everything you’re doing and jump on the reservation.
Keep in mind that this state park is the number one requested state park in their system.
If you pay for a premium membership - $30 for a full year - their system checks every minute for a matching opening.
I joined this site and bought a Premium membership. I got into a beach state park during spring break in one day. And, since then have gotten sites at sold out state parks two more times this year. I passed this on to a friend and he used it twice to get into some national forest campgrounds, too.
It doesn’t make the reservation for you, it just notifies you immediately of an opening.
There are other websites that do this, too. But Wandering Labs seems to cover more campgrounds than others.