btw---if the area is really narrow as you describe...you could just make the panel I described out of sintra itself--use half inch or 3/4, and flush mount the images right to that. skip matt's & frames, although I understand if you want that--but we did an exhibit like that, albeit in a larger area. we used one inch or so thick acrylic panels and face mounted cibachromes and b/w prints to the back of the acrylic, used silkscreen for the text on the back, so you viewed it from the other side and it was all very clean. these were big--the primary & secondary signage for an exhibit that was in a huge gallery (13,000 sf) with no walls except the outside ones. the panels sat out in the open, lit by spots--the images looked like they were floating. we used black sintra on another exhibit, but created oversized photo "albums" with the pages being made out of Sintra- mounted both sides on these. sintra is pretty durable stuff, but again--not "lightweight" nor cheap....but my point is, I guess, if you can move beyond the material as a substrate and look at it as part of the design, you might be able to fit something into that space...