I like the modulation idea but would add more, certain areas seems a bit two tone especially shadows looks like preshading which in tanks I do not fancy much and looks like makeup ... I would add some more hues to add more character and kill certain shadows, but good start mate ...
I think that it is looking great. Maybe less contrast between the low lights and the main colour. you can always respray the areas in the original colour.
is it done Rob or do you need to weather it more? Whatever you decide it looks really good, i especially love the exhaust with all the rust. Well done as usual.