The claim: Savannah area - FEMA designated detention facility
What it really is: Fort Stewart is a large US Army post, and also trains members of the National Guard there as well. The base also families living there, whom live in military housing units that are typical for bases of such size.
I've also taken a look at the satellite view of the base via Google maps, and none of the buildings there actually look like it something from a prison camp. Everything there looks like what you would typically find on a normal military base.