In view of what they are being used for, I would consider a secondary fastening, after all you don't want to take out a cyclist do you.
Off roading will really put a strain on the latch.
Why not an Anti luce fastner as well. Easy fix.
eg
http://www.ebay.co.uk/itm/NEW-12mm-...009?pt=LH_DefaultDomain_3&hash=item19c97603b1
Also consider some form of stop to prevent the wheel carrier from going sideways. You probably will, but put something in place that won't chip the paint, like a rubber bump stop etc.
Similarly for the closed position, to stop it rattling.
Why not put some M8 or M10 nuts in various places, for adding attachments later, bike rack,
extra spare wheel, high lift jack ropes.
You will also need to consider a bolt or something to keep it open, when opening the rear door, if you happen to be on a slope.
Just a bit of lateral thinking....
It should look very good,:thumb2