Let me try to ask it this way:

Regular double 18" PA sub:
Much weight in speaker, much weight in wood, makes great stack, good output.

Labsub:
Reduced weight in speaker, much more wood, makes also great stack cause of the same size as double 18", much more output (if i believe the guys from LAB.

Pi-sub:
Reduced amount of speakers, troumendous amount of back-aching MDF, makes poor stack, good output; but not very common in use with drive-in shows.

Regular double 15" sub:
Reduced weight in speaker, less wood, makes poor stack, lacks in output on bigger events.

What i`m looking for:
Reduced weight in speaker (use mag12 speakers), reduced weight in wood (not horns as large as the labsub), Sizes that do make good stack (lets say something as single driver cabinets, wich you can stack 2 high and X-wide, +/- 2 meters high with the top-speakers on top), great output.

Would something like this be possible?

Kind Regards,

Erik