Great spot for free camping (you do have to get the permit), and the best part is you can only get there by water!  We paddled from Ft Desoto (one on kayak, other on paddleboard) with all of our gear roped on.  

Once you get to the island, is is 100% primitive as it's a preserve.  Absolutely amazing with stunning views.  Others camping were far enough away that they didn't disturb us.

If you want an adventure leading you to an amazing camp spot, this is it!