A WD is needed when the tongue weight exceeds the manufactures hitch rating for weight carrying ability, when the rear of the tow vehicle sags so much that headlights will not aim properly, when the steering feels light or out of control, when you are exceeding the rear axle or tire loading ratings of the tow vehicle, or when the the trailer feels like it is taking control of the tow vehicle every time you hitch it up, or a combination of all or most of these.
My feelings are that you will probably not need one for the trailer you are considering BUT keep in mind that tongue weights are usually much heavier than described by the trailer brochure or specs by the time you are ready to go camping. Also don't know what you mean by a "considerable smaller truck".
A truck like a Ford Ranger may need one while a F150 probably would not. Many people are quite surprised when they eventually get around to actually weighing the tongue of the trailer.
Barney