Thanks for the offer of help Michael, I have this same problem with rhino too, which is why i came to MoI, so i know the problem is with me and methodology - No formal training so i must be missing something with the theory of it all :)

If you go back to the start of this thread you will see the two surfaces that have been zoomed in on on my last post, that they are sitting nicely aligned - The surfaces are either sweep or network surfaces, but they are fine. Once i start to slice up the surfaces (trim) for where the doors should be and to round off creases etc, then for whatever reason these surfaces start to move around as if by magic, I have tried ShrinkTrimmedSrf but it don't make a difference. The problem is I don't know when it happened or how, but because all the other trims, blends and fillets are done, and because i use surface edges rather then new curves where possible, the original alignments are gone.

On grab-04.jpg the right had trim line for the door has shifted the remaining surface segment from alignment without me noticing, but that one is easily repaired with control points or by deleting and using the new edge that got inserted during the trim process, the other surface - image4.jpg also shows how it has altered the surface curvature some how too.

The area shown in image2.jpg is perfectly fine in grab04.jpg despite having the trim going through part of the surface, but then some how during the process of;

Trim
Offset
Loft edges that need fillet
fillet corresponding surface
delete offset surface
join all surfaces created to keep everything as a group

Somewhere during that process it's changed it's position as if some sort of elasticity that held it in place has gone. I know it must be my technique. I don't single side sweep as i know it creates problems with continuity and accuracy, when i try doing vehicles I only use sweep, loft or network as you don't get many planar surfaces in vehicles as you already know. Is there a book you would recommend for me to read that covers Nurbs modelling rather than the maths, the theories and algorithms are way too heavy for my feeble brain ...

Many thanks

Martin