The NYPD has more than 34,000 uniforms and 8,800 cars across 77 precincts. Shifting even 1/3rd of a precinct into a mobile base would take a wee bit more than a couple RVs and some street side parking. Then you add in increased utility bills since RVs have a fraction of the insulation and much less thermal mass inside. And RV replacement bills from broken walls and whatnot (even the external walls are thin, and not exactly easy to repair).
No, I think structural anchors, massive ballons, and fusion powered thrusters to lift a building and move it would be cheaper than making the NYPD nomads.