I think this looks really nice. I like the weathering on the car. But if I may ... the car looks like it was just set on the base. I think two things would really help it a lot and I don't think that it would be hard to fix. 1) Mark where the wheels are and lightly dremel out an indention for them, as if they are sitting down in the dirt a little. And 2) tire tracks ... I think the easiest way to do this would be to dry brush a lighter color of the base paint back from the vehicle. Take notice too of how the front tires are turned, so they will actually have their own treads as well.
These are just suggestions. LIke I said, I like it. The only reason that I bring it up is that most "new" dio builders miss the fact that in a contest EVERYTHING is judged.
BTW ... are you taking this to Sqaudron's EagleQuest Show? Just curious ... I'll be there.