Semi-permanent resident is the correct term I think. Mostly a group of hard working folks that are away from their family most of the time trying to make a living working on the natural gas and oil drilling and distribution pipelines, ship building, port construction and many other type of jobs.
I have frequented a few campgrounds in my travels across the country and met a few of these workers while overnighting in the same park. A large percentage work long shifts four days a week and book home to their families on the weekend. Their campsites and rigs sometimes tend to not be kept up to the standards a lot of us sometime expect. Some of the places I have stayed started allowing this in order to remain open. Kind of off the beaten path parks but able to survive with the fixed monthly income residents. The few I frequented always had a good number of spots together for the overnighters. Always worked well for me and kept me from being on the road another hour or two after driving all day.
Just remember, everyone has to make living and you always have the choice where you stay each evening.