There is a great level of detail on the body of this model, and it will look even better if it can be highlighted in some way. This applies to pretty much all of the ready to run rolling stock available these days.
My plan for this shunter is to use a panel line wash applied to all the crooks and nannies with a rigger brush. What's a rigger brush? It has long bristles and a small point - some folks call it a lining brush. The idea behind using this type of brush is that the bristles hold plenty of paint, but the small tip allows it to be applied with a degree of precision.
The wash I am using is Ammo by Mig Black Night, but you can use any dark colour to achieve the effect. The process involves dipping the brush into clean thinners (in this case white spirit), dipping the brush into the wash and removing the excess (the blob on the tip of the brush). The tip of the brush is then touched to the corner of a panel or edge of a door/window moulding, and capillary action takes the wash along the detail. Easier to do than describe!