This is a flat pack for an 18" woofer - sealed 90L box. It is designed to go into a corner under a horn, but it could be used for other systems as well.
CNC machined for easy assembly, with trenches machined so pieces fit together nicely and bracing also slots in.
The design is similar to my prototype:
The prototype above was built manually. I no longer have time to build things this way, everything now with CNC.
Shown with a smaller Unity horn.