DW & I live in the area, but we have never considered camping on the Beach because we like full hook-ups.
We enjoy Brazoria County Quintana Beach Park (next to Surfside Jetties), Brazoria County San Luis Pass Park (these can be a little close together, but great fishing location), and the newly opened Bluewater RV Park (2 miles from San Luis Pass).
I'm a diver, with numerous certs including helium for open circuit doubles and normoxic for closed circuit rebreather. Diving offshore can be good under oil rigs once you get 20 miles out. March would not be a good time for rig diving. The Fling might be running trips out of Freeport to Texas Flower Gardens for annual hammerhead migration, but I have never been in the Gulf outside of June - September.
Five shops have opened and closed in the Brazosport area during past 25 years.
SMSgt USAF Retired
2001 Tiffin Allegro Bay 36DB, CHF, Bilstein B6 HD shocks, BlueOx rear tiger-trac
'13 Jeep, '12 Victory Cross Country Tour, Hollis Prism2