Looks like theyre #3 on the list
http://dmv.ny.gov/forms/mv274.pdf
XAMPLES OF TRAILER-TYPE
VEHICLES THAT DO NOT HAVE TO BE REGISTERED
Not limited to these vehicles
Welding machine mounted on a chassis
Well drillers mounted on a chassis
Wood sawing outfit mounted on a chassis
Wood chipper mounted on a chassis
Electrical transformer mounted on wheels
Air compressor mounted on wheels
Water pump mounted on wheels
Pipe threading machine mounted on wheels
Concrete mixer mounted on wheels
Generator mounted on wheels
Portable lighting units mounted on wheels
Paint outfit (air compressor and tank) mountedon wheels
Insecticide spray outfit mounted on wheels
Portable sheep dipping vat mounted on wheels
Trailer used as an office on a job site
Trailer used for tools and equipment whenequipped with shelves and bins, etc., on ajob site (shelves and bins must be empty
when towed on the road)
Food vending trailer (shelves and bins must beempty when towed on the road). For example,hot dog cart or a barbeque grill on wheels
Tow dolly
Tar kettle mounted on wheels