Really though, you should never use only one layer in PS, especially for something as potentially complex as a profile. It would be a nightmare to have to correct a paint color for example, if you had already shaded and weathered it. A layer for paint, a layer for markings, a layer for shading, a layer for weathering, etc., is the way to go.
As for tutorials, there's a good step-by-step progression over at Mil-Mesh here: http://www.military-meshes.com/forums/arti...article&artid=9