In Reserva Forestal Toro Negro, near the ranger station in Area Recreativa Doña Juana, this is a designated camping area with enough space for 14 tents. It's up above Hwy 143 by a defunct swimming pool that in its heyday made this a more appealing spot. Get a permit from the DRNA in San Juan. Apply 15 days in advance.
If you bring charcoal and lighter fluid you can cook your food over one of the open-air picnic grills at the Area Recreativa Doña Juana.