Wife and I looked at a park model-only resort a few times. They told us clearly that full-time living was prohibited, which they enforced by not allowing mail delivery and probably other means. Besides being their rule it also violates local zoning (this is Pennsylvania, a relatively high-regulation state).
In most parts of the country you can't live in your vehicle, full stop. RV's are titled vehicles (as are park models). Mobile homes are deeded and have to meet HUD standards and are different legal animals.
That being said we've all seen 'campgrounds' with obvious full-time RV residents. Around here it usually boils down to location. Rural townships are more likely to let something like this slide. No resources to enforce the laws and residents that don't care anyway.
My question is, why buy trouble? If local laws prohibit what you intend to do and you plow ahead anyway, you're asking for problems sooner or later.