First, we'll create some procedural textures in Blender. These will be the base textures (not the final product).
After we do that, we'll create and adjust the UV map for our truck.
Then, we'll bake the textures to an image using our UV map. We haven't covered baking yet, but it's pretty straightforward. If you're already familiar with the concept, then great! If not, don't worry, we'll discuss it as we go.
After we have our image-based texture map, we can tweak it in an external image editor and add details.
Finally, we'll use that image map to create Cycles-based materials for the truck. This last step isn't critical, since the truck model is intended for other applications (not Blender). But it's a good way to verify that everything lines up and works as expected.
So, let's get started.