Though many ordinances allow this there must be some somewhere that made this a state law:
NC is about to approve a bill requiring all jurisdictions permit Temporary health structures as accessory structures to a primary residence.
Temporary family health care structure. – A transportable residential structure, providing an environment facilitating a caregiver's provision of care for a mentally or physically impaired person, that (i) is primarily assembled at a location other than its site of installation, (ii) is limited to one occupant who shall be the mentally or physically impaired person, (iii) has no more than 300 gross square feet, and complies with applicable provisions of the State Building Code and G.S. 143-139.1(b). Placing the temporary family health care structure on a permanent foundation shall not be required or permitted.
aka. you can pull a single wide on the property as an accessory structure so you can take care of a family member. Also lets Johnny live on mom and dad's property because they are ill.
It will be interesting to see if some rural areas are overwhelmed by this one in the near future, though I don't know if you can get a 300 foot single wide and I'm pretty sure a fifth wheel doesn't pass State Building Code for residential structures.