Yes, the black coach is still a fiction of my army, but yesterday I've been building a prototype out of cardboard to check for scale purposes. I felt like a genuine arts and crafts wizzkid building his own foldable dice as the entire model was cut out of one piece (at first).
I used google sketch-up to make a basic print (free software) of the fold out without flaps with you can download here (for all those leeches).
The ornamentation will probably be made of greenstuff while I'm still looking at dollhouse things for the ornamental metal brackets that suspend the driverseats and such.
Keep you posted.