Looks pretty good. Don't spray it with a black wash though. Never use black on desert vehicles, it is way too dark. You should do a pin wash, only applying wash in selective areas such as panel lines and around bolt heads, with a dark brown color. Then give an overall wash of a sandy color. Lastly, drybrush it with a light sandy color to make it look more dusty.
You have a pretty good start. A bit more weathering and it will look great.