I use This if I want to bag my trike.
Thanks for that - exactly the sort of info I was after.
That bag arrived this morning, and I've had a brief play. Barakta's trike will go into the bag easily by just folding the back over, leaving plenty of room for the seat (and anything else you feel like stuffing in there), so that's a win.
It's a monstrous piece of luggage, though. Reasonably stable, with the trike lying on one wheel, but not exactly easy to lift (barakta wouldn't be able to without injury, I don't think), and falls foul of the Conditions of Carriage 90x70x30 rule by a fair margin. I can see actually getting it on and off a train being a bit interesting, too.
More enthusiastic dismantlement would probably get it down to size, at cost of faff and stability.