You said it is register. Does that mean you were issue a license plate? I would think if you have a license plate issued you wouldn't need fenders.
My father-in-law built be a trailer a few year back and it doesn't have fenders. I had to take it to the highway patrol for inspection before I was given numbers to stamp on the tongue and axle then go to the license plate agency to get the tags. Now with all that said, I live in North Carolina.