The third COE we have stayed at on J. Strom Thurmond dam. (Basically we spend a week at each cos of limited availability) We stayed in GA and SC sides of the lake and two out of three have great cell coverage on ATT and Verizon - this one is great in that regard. Guess it can vary from site to site , so check it out. ( we were in #21) Great walks, also beaches and boat ramps. Definitely will come back to these delightful COE.
We do not use showers and restroom facilities so cannot comment on them