Don't know if your trails will take you near Chrarleston, SC, but if it does, James Island County Park is a wonderful place to stay for several days.
As for Savannah, we stayed at a no-frills campground in Hardeeville, SC called Hardeeville RV
. When I say no frills, no shower, and the other facilities you may wish to use your own. FHU. You will have to negotiate your way through the trees to park, but it was worth it for me in our 40' MH. It is 9 miles from downtown Savannah, and close to Beaufort and Hilton Head.
Edited: p.s., Garrison, TX is not to far off your route and about 188 miles from Dallas. There is a herd of deer there that will eat dear corn out of your hand. Axis deer. Very peaceful setting and a natural spring pond. Inexpensive also. Camp Tonkowa
(used to be a boy scout camp.)