Quick update about things I'm not supposed to be doing while I should be packing to go away...
If you'll recall, the size of the build was essentially determined by the largest piece of wood I could buy from Homebase. Well, today, I went and bought that wood and can announce that work has officially begun on the body of the AT-AT.
The next problem is the building of some kind of frame upon which to fix the panels to cover the body. There are many (better) way of doing this, but after some digging around in the shed I found an old clothes drying thingamajig which I'd been keeping because It Might Come In Useful One Day.
I've drilled some holes in the base for the thingamajig to slot into and (hopefully) this ought to be strong enough to support a cardboard shell.