The state (MN) DOT gives great latatude to pickup's pulling goosenecks and bumper type trailers. If is even slightly resembles a farming activity, they generally don't bother. About the hardest compliance would be a health card.

In the same breath, it's not hard or time consuming to get a Commercial licence. Takes all the questions away, as far as farm use or quilfacations, from the DOT, when stoped or checked.