I am making progress in my own steady way. Today wasn't the ideal day to be outside cutting 22cm lengths of pipe for the ports.
As the cutout for the speaker was a bit big and so the fixing holes were precariously close to the edge, I glued in some short lengths of reinforcement and then drilled for T-nuts. Remembering what had happened with the BC 112, I checked that all the T-nuts threaded up, then put them in place and tightened with the speaker in place so that if any finished up slightly skewiff they'd still go in.
Still to do - put in wadding (on its way), glue in ports, put top on, round corners off, filling and sanding, and covering - I have a good-sized piece of leatherette left over from the BC micro cab which I'll use for that. Plus cut grille to size, put connector panel in, wire up speaker and put that in.
Reinforcements and T-nuts placed ready for initial tightening:
Box with bottom attached:
Inside view: