Well, I don't know anything about Filleting or anything else you said, but here is the way I would model a nurbs door. This is the easiest way in my opinion. The first image is your door made from a nurbs circle. It is one whole object with one isoparm traveling around the exterior edge, which might be helpful in some cases. This proceedure is accomplished by smoothing the poles of the circle with the Smooth tool in Edit Nurbs?Sculpt Surfaces Tool. This can be easily done in the top view. You then take each vertice and position it so that it is parrallel with all other vertices on an axis. This is probably the hardest and most complicated way to model a flat surface.

The second image illistrates your door made mostly from one single nurbs plane. You simply take the vertices and model a little at a time, inserting isoparms along the way to give you more to work with until you make the two ends of the plane meet. There is no way to stick or combine these two isoparms, so your only choice is to patch it. Create a plane (the green one in image 4), position it in between the two ends, and stich it.

There is another way as well, which caters to a door model that will be attached or stiched to other parts of the truck. As you can see in the third image, the door is made up of 4 nurbs planes or "patches." You can stich these together, then select exterior isoparms on specific patches to connect other parts of your truck to the door. Modeling a patch door can be done either by creating several plane, then positioning them into their proper places, or by modeling what you see in image 2, selecting several isoparms, then choosing Edit Nurbs> Detach Surfaces, THEN recombine the patches by stitching the isoparms together.

*whew* You probably didn'y understand a thing I just said did you? Read it over a few times. Anyway, I hope this helps in some way.