We have camped PINS twice. Both times were great fun, went to the 10 MM. I do have a 4x4 but only needed it the second trip ( saved our hides / high tides from Hurricane in the gulf / saw 4 RVs lost to the surf.) Usually, the beach driving conditions are fine for 2wd. Call ahead for driving conditions. The best part is the solitude. You have to bring fresh water. PINS fee is $10 good for 7 days. If you get there after hours, well...it's free.
We have also camped at Padre Balli Park, a Nueces County park with 2 shower houses. Tent sites were about $8/night. If you take a tent site in the Camping/parking lot with grass, you have to use the pay showers. If you camp in an
rv site, you can use the free shower house. The loops are just behind the dunes but it is still very windy and even more humid. There is a great fishing pier called Bob Hall where I've spent countless hours last summer fishing. Its lit and open all night. People catch sharks off the end, and reds, trout, pompano, whiting, and others all along the pier. They have a concession stand, tackle rentals, boogie board rentals, bait, and misc beach gear. If you are traveling with kids, this is where I'd go. If it is solitude, go down PINS, 4 1/2 MM should be nice. Pack light, and if the sand is soft, don't stop.
I haven't camped Mustang yet. But, the facility map looks like Turnkey said, like a parking lot. If it's me and the family, we do PINS, if it's just me and my son, Bob Hall is the place. If you pick Bob Hall and change your mind, the Best Western on the Island was $86 night, 7 minutes from the pier and continental breakfast. Those nasty looking motels are $55! The circle K on the corner of Park road and Whitecap has cheap ice.
All this talk makes me want to call in sick and go coastal!
Have a great weekend and be sure to post up a report upon your return.