The link to the larger image doesn't seem to work (might be my end though) so its a bit hard for me to see how you have constructed your model. Personally, if I was building a car, I would construct it similarly to how a real car is built, from separately moulded and fabricated panels and parts. For example, I would construct a door by extruding its cross section, then tweaking the nodes as necessary. Sure, this is a difficult way to build something, but the finished model would be excellent.
Alternatively, you could consider building separate internal panels, shaped to fit perfectly inside the car and giving the doors and panels thickness. It would help if you could post a larger image of your car showing the wireframe.