Thanks so much to all that have looked and commented - I really appreciate it!
I've started the weathering process by airbrushing a faint amount of what I call "Greyish dirt" (Tamiya acrylic paint mix of all sorts) all over the model, concentrating on the lower portions and the rear of the vehicle. This tends to make it look quite toned-down and bland. I have then dampened the surface of the model, about 2" at a time, and applied a mineral spirit wash of brown/black oil paint to the details. I went over this a few times with a dampened brush, streaking it downward. It needs to be done over to help blend everything and get rid of tide marks. Some tide marks can be seen where I've started on the model.
This is just a couple of steps in a long process, but I thought I'd put up a picture showing halfway progress on one of the sides as an example. Still lots of steps to go.
Model airbrushed with greyish dirt colour, and oil paint pin-wash started on the right hand side...working my way to the left.
Cheers,
Gary