From: bjfish11 - enclosure material question

[///M5 2,833]

If you want lightweight, Baltic birch ply in 3/4" will be the same or less weight than a 1/2" mdf enclosure.

Considering weight & SQ are your paramount issues, I would 1) Limit the enclosure material weight, obviously IB is best, small sealed 2nd, 2) Pick my driver based on what it can do, but also with enclosure size as part of the equation, 3) Limit the overall weight of the driver as this will make a HUGE impact on the overall weight.

So what am I saying? I'd use a different sub and just a single one. That will give you more weight savings than looking at just the thickness of the enclosure. If you do use both, I would argue that you aren't that concerned with weight really.