Awesome job, Alan.
My first bucket is nearly complete - waiting for the concrete to hydrate.
While I am waiting for that, I played around with some box calcs for this Peerless 8" sub:

y36c

This plot shows that sub in my sealed box (0.5 CF is about what's inside the bucket), and in a 3 CF vented box. What a difference!
What I don't know is what WinISD is doing regarding box shape and how it would differ if it could model a cylinder.
Perhaps the next experiment is to take a 40 gallon brute trashcan and try out a 12" LoL!