Here is a little break-down of my Defiant textures.
I always use a layer with the UVs for guidance.
The first layer is the color layer. Not much to say about it. Painted by hand or baked from the colored 3D model, depends on the UV layout.
The next would be a random panel layer, but the Defiant does not have any subtle paneling. My luck, this would have been the most time consuming layer.
So the base dirt or noise layer is the next. This is a texture from the internet and multiplied on top of the color layer at 10% or so.
The second dirt or noise layer is a metallic texture with some rusty marks that is masked by an alpha map rendered out from a curvature shader. Parts of the texture are flipped upsite-down to match the orientation or the UVs. If you close look at the rusty marks you will recognize it. This layer is multiplied on top at about 70%.
The third noise layer is another rusty texture masked by an alpha map rendered out from an ambient occlusion shader. It is multiplied on top at about 50%:
And here is the final result:
By the way: all decals are modeled on top of the main geometry.