Howdy, this is a separate question from a project which I'm working on. I'm struggling with how to make the grooves and hollow incisions which seem carved in a flat surface?. This happens when there is a discontinuity due the two objects have been placed together.

In my project the part which is contiguous to the front door and the back end of the VW bus look like is sinking inside the surface. How to achieve this effect?. This is seen in the arrows pointing in the image and the rounded portions.

I've attempted to retrace the object by drawing a bezier curve but the result is just a flat color.

Then I've attempted to duplicate and increasing the stroke to use it as a shadow effect but this didn't made the effect the way I wanted. The problem arised in the curve, as the "shadow" seems to go along the initial stroke from the bezier curve. Therefore my question. Does it exist a better way to achieve this?.

In my effort to look for an example of how the light goes in the incisions I've found this picture of a real VW bus which has the matching colors of the profile which I'm drawing. 

From it looks as the joints caused by the discontinuity of the doors stick in while the frames in the upper windows stick out and the windows in the passenger line are sticking in.

In general I'm having this problem when trying to recreate this effect when happens in the doors from cars and lids or any other coverings over the hood.

Can someone help me with this?. In the example this carved effect goes between white and redish orange colors in the VW bus, and it seems to happen the same in the windows. How can this be recreated without much fuss?. The problem is how to get the right ammount of light so it matches the example?. Can someone help me with this?.

Maybe like so: