I guess I should have given a little more information. The board is a big. REAL big. Around 4'x6' and will be hung in a hall in our church for the Cub Scouts leaders to put stuff on. Foam core probably wouldn't last with all the stuff that will be put on and taken off. I imagine rigid insulation would be the same. Most boards have a fiberboard backing which isn't as dense as plywood, but much more dense than foam.
I tried some rougher plywood today and it seemed to be alright. It was a little tough getting the pins in, but not as bad as before. I think this will do fine and may actually stand up better over the long haul.
Unfortunately for me, I got in too big a hurry and "assumed" my plywood was the size I thought it was. I built the frame and got ready to set the plywood in, only to discover the plywood was an inch too short!:BangHead: Seems I forgot that the piece I was planning on using for this was a piece I cut a while back, telling myself I would adjust the frame when it got to that point. Well, guess what I forgot to do!!
So, I had to take the frame apart and cut the long rails again. I will glue it up tomorrow and see if I can get it all together before my kids go off to college!:-?