I was hoping to get this done sooner, but some of the parts took a while to arrive. They're here now, so it's all done.
I also have to say that this the most awkward build I've had to do.
We'll start with the lower section. The baseplate is 48x48, and the first two walls are 1x2x5 panels, with 20 on one side, and 19 on the other. Next is the start of the Technic frame, then filling in the walls. The gap is there for a reason.
Now the top of the Technic frame, made entirely of 6x8 and 4x6 (and pins, of course), and then come 24 7-beams, 23 of which have pins in each end. The empty one, and two pinned ones are used to attach a 16-long Technic brick, whi