Thanks very much for the tips Michael.

I'll clean up some of the geometry and see how that goes, makes sense that 'wrinkles' would cause problems, not sure how I ended with them though.

With the tail-end I tried to Loft the tail the same as the nose (to an end point) but the Loft function didn't want to play ball. Actually the Lofts (on the four curves) seemed to be governed a little by the general happiness in the universe (ie: random) with a view change (zoom out seemed to help) sometimes causing the loft to succeed or not, but perhaps my swooping long-curves caused problems? I'll try the plan-off the end and see if I can then fillet it back to a softer 'cap'.

Will report how I go. Thanks also for the fold-over link I'll read that as well.