I have an artist that created an "Artwork" by painting on 2 separate pieces of thin masonite - each 3 feet by 6 feet. She insists that she wants the piece mounted in a single frame, with one board on top of the other. She also does NOT want any glazing. Besides the fact that the final project will be 6' x 6', how do I keep the seam together? The board is so thin, it bends and buckles in the middle.