Now I'm thinking of making a deluxe folding DM-screen model based on Maplin's lightbox, but I'm not sure how to go about it. First thoughts were to go with reflective sides again - two pieces of foamboard on thin wood, maybe.
If you use wood for the 'frame', maybe you could buy some small hinges. That way you should be able to fold the construction. You have to decide on the thickness of the foamboard/wood construction first though and probably visiting you local diy before you start constructing your new lightbox wouldn't be a bad idea neither.
.:edit:.
You could also use some little clamps/ clip thingies like
these on top of the backside, so you can easily change the backdrop from standard white/blue gradient to something else.
You could even experiment a bit using some
cardboard with mirror finish for more light, if you have only one lamp (I once used some cardboard candy container, was ok, if a bit bendy )