If you do decide to use a WD hitch, consider a Blueox swaypro. They sell bars as light as 350 pounds.
The trailer will likely tow fine without a WD but with one, it would probably be a smoother ride in the truck.
EDIT: further thought on this. I've towed both my funfinder travel trailer and my horse trailer with this Nissan Frontier. Both on the ball, and using the blueox swaypro WD hitch.
Nissan specs that under 4500 pounds it s acceptable to tow simply on the ball. Over 4500 requires WD. This FF is 4100 loaded. The horse trailer is 3900 empty.
However, using WD does exactly as the name implies. It "distributes" some of the weight from the tongue to the steer axle and back to the trailer axles.
The result is a more balanced combo rig, resulting in better handling and a more controlled and smoother ride.
To the OP, I'd say it's your choice to tow it either way, and be within the guidelines, but you would likely find using WD to be an advantage.