The first ceiling, is a fake ceiling to cover the pipes and electrics, and give support to suspend the second ceiling. Built in the same way as the previous one, wooden batons round the circumference of the room, with three cross-batons resting on them.
The ceiling is MDF, sprayed with an enamel gloss white paint. About a thousand layers, and it's still not perfect.
I found some simple right angle brackets to use to suspend the second ceiling, and fitting these to the cross batons with bolts, and big nuts and washers on the other side.
Overhead piping just came through at a right angle with a push-fit elbow, and mains cables (lighting circuit) with a bit of ducting.
Trickiest bit was getting it in place. A single piece of MDF was pretty big, and we had to get everything to line up; the pipe, the cable, the speaker cable, and the 6 bolt holes. Was very tricky, but we got there after a few attempts.
Looks like this now:
Not a bad job, if I do say so myself. A few gaps here and there, but coving will cover those. And importantly, the brackets are on solid, with all the weight being distributed across big washers, and the lateral beams.
That's also a waterproof plug socket that I will plug the lights into. It's fed by the wall switch panel. It's rated IP65, crucially, when
in use. I found some that were only rated when not being used, they're for sale now if you want one.