In fact ... skinning that way ... will not give good results mostly.
Without the wireframe, it is very difficult if not impossible to be aware of the car shapes and forms.
The second problem is mostly the .... ambient occlusions.... a apart layer in a template ....
In a dds.file ... there's just 1 layer and the same color has different nuances due to the influence of this apart layer in psd ( or xcf for Gimp ) when merging all layers.
Very difficult to get the same effect .... if you have to do it manually ... and those nuances are very important to get a good result in game.
Learning how to create a template ... using 3dSimed and Blender helped me a lot in this case.