As I understand it, Typical stuffing for BIB's is from the point to just above the driver, and a layer on the bottom of the bend, with some directly behind the driver to mitigate reflections through the cone.
I'm getting ready to make some sawdust on a pair for one of the Recession Buster 2 kits I bought last month.
My plan is to line the front of the divider in the area of the woofer, and the bottom of the bend with some acoustic foam, and tease out some poly to put in the top above the woofer.
I'll let you know how it went when I finish.
John