What is the sunbelt to you? East of the Mississippi I've found complexes of home like this as far north as Tennessee and all the way to the Gulf Coast and in Florida. Between the Mississippi and Rockies, starting between Dallas and Austin, south to the Rio Grande.
Most are ownership communities, not resorts with rentals.
Many communities will also allow you to build a RV garage, but most building codes do not allow you to live in the RV permanently. It can be difficult to write a building code that allows this and still prevents lapse of the neighborhood into a trailer park, thus you more often find the RV ports in planned communities where the discipline comes from a property-owners association or other types of contractual covenants.