As SRDS noted that is a loaded question, the parks link on the left of this page is a great thing to use. Now saying that we live in North Texas also and camp in a 22 ft Hybrid. Within a short time distance (less than 3 hours) are a wide variety of nice parks. (Send me a PM if you need more)
March should be ok for almost of them. So here is my list(NORTH PARKS only)
Cooper Lake South Sulpher (we went there in August)
Cooper lake SP South Sulphur Unit Review
then Fairfield Lake SP
TPWD: Fairfield Lake State Park
and finally Lake Tawakani State Park (use the link from this site under parks)
Both Ray Roberts parks are close and have lots to offer, and in March should be ok to visit, they get full because they are so close to big D and Ft. Worth.
Dinosaur Valley is a small park, (which is one reason it gets crowded when it warms up) but it is nice if you want to hike and see the dinasaur footprints. It has plenty of shade and you can walk anywhere from most of the Water electric sites (no full service sites ). I am sure you will get lots more
