Hi Jeff
I realise that this is not an answer to your question, but I use MDF fibreboard, roller-painted with a sealer/undercoat, and the print attached with Scotch 568 positionable adhesive. I use a router to shape the edges and paint the edges in matt black. This gives me considerable flexibility with sizes and thicknesses.
I don't know how archival this is, but I hope that the use of sealer/undercoat will prevent degradation of the print, at least in the medium term. I have decade old prints on unsealed MDF. The only issue is the spray adhesive has let go in the corners of a few of the prints. I'm hoping that the Scotch adhesive will be more permanent.
Bob