Wiki has a good piece on bike dampers, and they are fitted at the factory.
Nissan din't see fit to fit one to the T2, Blandrovers all have them I think however.
I've got big simex tyres on mine now and a lift and apart from the wheels being a bit out of balance, which I will get sorted I have no shake or wobble at any speed or on any surface. Well apart from at slow speed when you can feel every knobble on the tyres but a steering damper wouldn't solve that as its up and down.
Its my feeling that a steering damper on a T2 could actually make maters worse as it could push the transverse link rod in another direction, and thats the big problem with these the movement of that rod other than side to side.Of course with the link rod mod done there would be no problem but on a standard truck?