Thanks for your kindness,everyone.
Now that Bibbster has sorted me out with photos, there are a few things that might interest those planning to make their own.
The top surface and three sides of each half are 3mmMDF, but the fourth side is 2x1 inch softwood to allow the use of reasonable length woodscrews for the hinges.I used white woodworking glue to attach the sides after gluing the MDF to the foam with solvent-free glue of the 'No More Nails' type.
You can just make out the little pads of Velcro that keep the flower beds in place on the ends.The middle bed with the flagpoles just sits there located by the rebates for the hinges.
I wasn't going to put a board backing on the hinged section, but ended up doing so by 'accident' as my first attempt at routing the track was a disaster! :oops:
The power supply is a plug-in regulated supply from Maplins(a UK electronics chain like Radio Shack), with switchable voltage in steps from 3.5v to 12v.I used a 60ohm Carrera controller(E-bay); and you can't really use more than 9volts.
I did wire an on/off switch to an XLR plug which can substitute for the controller , which lets you run a car on low voltage without attention.Like under the tree at Christmas, for instance.
The perspex barriers that stop the cars falling over the edge are held on by neodymium magnets like the ones you don't need in cars if you run on wood. One magnet fixed to the frame with adhesive mounting tape.(N.B. TAKE CARE HANDLING THESE IF YOU HAVE A HEART PACEMAKER - and don't get them within a foot of your credit cards).
That's it.
I'm hoping to try a bigger track using the same method next.
David.