The paint job was really easy - I’ve found that Acrylic paints are great for weathering, the fact that they are water based makes them far easier to work with.
I used a colour called Anthracite (a greyish black), and a faily stiff, medium width modelling brush. I slightly watered down the paint and liberally applied it over an area of the craft.
As soon as I had appliued the paint I got a piece of paper kitchen towel and wiped away as much of the paint as I could. This left paint in the inaccesable areas, around detailing and in the panel lines. If I wanted to exaggerate an area I just used the paint neat.
Just be careful not to paint too large an area as the paint dried quickly.