In a project I work on, we've had to "dumb down" our 3D models because there are hundreds in a drawing. I suggest creating the entire body of the car as a single object. Then subtract half a cylinder to represent the wheel wells, ditto for the rear. Add wheels. Additionally, you could also subtract the windows and add another solid the same shape of a different color. You can experiment with both 3D solids & blocks to see which is smaller.