We've heard of those; even stayed in one once.
As an example, here is one: (Its actually owned by the owners of the Petoskey KOA just down the street)
Rental Reservations - Hearthside Grove
Hearthside Grove Motorcoach Resort is a Class A only RV resort with restrictions on length (30′ or greater), age (10 years or newer), and pets (max of 2).
I saw another one in Michigan that had similar rules but would make exceptions for "exceptionally restored" vintage units (e.g. Airstream, etc.).
(We've never stayed in Hearthside Grove; we did get a tour of it when we were at the Petoskey KOA and they were offering tours showing their new property. As part of the tour they were showing a $1M Prevost motorhome.)