In reading up on it a little more, it seems as if they're trying to leverage the "PMA loophole" as a means of being exempted from the fair housing act.
I would expect it to face legal challenges (although, not sure who would be fighting to gain entry to live on a 140 acre campground with well water and a bunch of racists)
But in a nutshell, they're leveraging (at least for right now) a similar loophole that certain HOAs use to discriminate based on age or child-having status.
For instance, there are HOA communities that exist that will outright refuse to allow the sale of a house/land within the community to someone under the age of 55 or who have children living with them.
There are also some others that operate in the grey area like Orthodox Jewish retirement communities, where they don't directly come right out and say "No non-Jewish people can live here", but they structure rules in such a way that it accomplishes the same thing.
-- For instance, HOAs can require membership in a private club/organization as a pre-requisite for living in the community (much like some can require membership in the on-community country club), some require synagogue membership.
-- They can make it so all communal spaces in the community have to conform to Kosher rules and Shabbat-friendly code of conduct.
Ironically enough, there's actually a Black group trying to do something very similar in Georgia.
en.wikipedia.org