My husband is an architect and part of his job is recommending certain products for construction. One of those products is glue, and he has decided to go right to the top for the answer to this sticky problem. Forrest Products is the ultimate authority on glue (they set the standards for the industry). He happens to know someone there, so I should have the definative answer on archival glue for wood products soon. I guess I should have asked him to begin with.
Here is the back of the panel, all the mitred joints have little "footballs" inside (don't ask, I don't know). We looked at many different types of bracing, and I consulted books and websites. Everyone has an opinion about how to do this, and they are all different. So we are trying this, it is solid as a rock and smooth on the edges, so if I decide to, I can paint the edge and not use a frame.
When I get the answer back on glue I'll post it.
Jean