We are also working on a new hollow-back (the thing that creates a massive cavity on the backs of huge holds). When The Boss was made of polyester, the hollow-back couldn't remove too much plastic, or it would compromise the over-all durability.
But Polyurethane is way stronger, so we can have thinner side-walls on the hold. There is a "rib" down the center of the hold, for a little more structural integrity. We will have to wait for the first pour to see how much plastic is removed, and therefore, money saved.
If you look at this hollow-back, imagine that this is the "void" area on the back of the hold. That sounds like something Buddah would say: "Imagine if something was nothing". That's deep, yo.