Never done one this big, but I'm thinking how I might tackle it.
To give the raised effect, you could use foamcore. To make a piece big enough use separate pieces of 5mm thick. Then stick another layer to this, but stagger the joins. You then have a huge sheet 10mm thick.
You can then hinge the paper with tabs passed around the edges of the foamcore.
For the backing, I would consider using stretcher bars covered in thick Hessian. This might look OK as it is, or you could cover this with a another finer fabric. If you don't like the fabric look, you could mount primed canvas to the bars and paint the border with acrylic.
A thought occurs that while you were laminating the foamcore you could embed wire in the center so that you have a few 'tails' protruding from the back. You could use these to pass though the canvas and knot them at the back. This would avoid gluing. Might be a tad tricky getting the borders even though, but I think I know a sneaky way to do that.....
As I say, this is all theory but if it worked you would have a good stable structure that would be relatively lightweight.
