Everything that you see from the exterior view, has to be part of the exterior model.
Everything that you see from the interior view, has to be part of the interior model.
They are completely different entities.
What I usually do, is completely finish the exterior model.. then copy it and remove all the polygons that can't be seen from inside the airplane.. (underside of the wings in a low-wing airplane, etc,,).. and use that as a template for the VC.
The VC (cockpit) itself, is much more detailed than would be needed for an exterior view of the interior.. But wings and such (that can be seen from the interior), need to be as detailed as they are in the exterior model..
confused yet ?