The claim: Located east of Columbus near Alabama state line. Rex 84 site - Prisoners brought in via Lawson Army airfield.
What it really is: Ft. Benning is a huge army base, and currently supports more than 120,000 active-duty military personal, their family members, reserve component soldiers, retirees, and civilian employees.
After using Google maps in satellite mode (and street mode when available) I could only find a few buildings that might be mistaken for a prison, but upon closure examination I found out they were actually garages and warehouses for holding military equipment and vehicles.
Considering the fact that so many people are there (many being civilians) and the fact that it is right next to a major city (Columbus) it seems highly unlikely that this would be the site of a FEMA camp, or that such a site could be hidden here in the first place.
Also it should be noted that it is unknown if this was a Rex 84 site (or if there were any Rex 84 sites to begin with).