In the past, Park Models came with a sliding patio door as the main entry door. They did not have holding tanks as they were intended to be plumbed directly into a sewer system. The toilet was a residential flush toilet, with the tank that hold water, and they all had residential refrigerators. They were intended to "park" but still have a similar feel as a travel trailer.
Time changed and travel trailers, fifth wheels, and even motor homes are now equipped with residential refrigerators, and have come around resembling a stick and brick house on wheels, but retained the standard features of any RV.
Fast forward again, and more and more fifth wheels and travel trailers, and motor homes, are now being factory equipped with all electric stoves, hot water systems, and refrigerators. Again, blurring the lines between Park Model and transient RV even more.
Meanwhile, Park Models are now equipped with push peddle toilets and holding tanks. Thus blurring the lines again between Park Model and RV.
As travel trailers and fifth wheels become more and more like a house, they can (and are) set up permanently in Park Model sites and seasonal campground sites. The lines are blurred even more and more.
Park Models usually have a full front residential style set of windows. This is another item that separated them from RV's. But even now, some travel trailers and fifth wheels have introduced the front window again, although they are advertised to be automobile grade windows, like an automobile windshield. I certain hope they are, because I have one in my fifth wheel.
More and more travel trailer and fifth wheel brands are advertising their models for full time living. I learned what that means is .... yes they are designed for full time "living", but not full time traveling! If they never move, they are great. When they hit the road, they fall apart.
The lines are blurred. I suppose it's up to the campground, or the RV park if they accept any certain type of trailer, RV, or fifth wheel for long term parking.
2019 Montana High Country 375FL Fifth Wheel
2014 Chevy Duramax HD 6.6 - 3500 Diesel Dully Long bed Crew Cab