So after some experimentation (trying to avoid going back to the kaigoss mod at present).
I've found the following sub calibration results
1) Sub in trunk -- Boomy and overpowering
2) sub in trunk with seats backs down -- middle ground
3) sub in trunk with seats down and trunk open -- best so far...
4) yet to try - kaigoss II mod -- sub in back seat.
I can say that during this experimentation, I heard a lot more frequency range in the sweep...the MS-8 is supposed to level match from 50-80hz, but it seemed more like up to 500hz...information that was getting blocked by the rear seats.