Well that is different to the British versions. The canvas is fixed with turn buckles around the edge of the box and the switchboard is mounted directly to the box/headboard.
Here is a shot that shows the three fixings and earth strap. Strangely in those other pictures of mine, the bottom bolt is absent?
Also I'm guessing the two top fixings must be outside the switchboard cabinet. Can I just see the left hand fixing in one of the pictures?
And I've started by ordering 4 strap hinges off ebay, So cheap and free deliver, that it's not worth visiting B&Q! I've scaled the hinges at 4".
http://www.ebay.co.uk/itm/200906367104?ru=
I'll wait for these to arrive before I start pestering my local fabrication firm for off cuts. Ron