I made a design "wall" with cardboard bolt centers I got for free at a quilt store. You need six that are alike, which can be hard to do. Maybe some nice quilt store lady would save some of the same kind for you.
I laid three of them side by side, and secured that with duct tape. Then I put the other three on top the other way. Taped that and taped the two layers together. I made a "pillowcase" cover for this of flannel, light on one side and dark on the other. (I've never used the dark side. LOL) When I pulled the cover on, I was expecting to sew the opening closed by hand, but I was in a hurry, so I pulled the edges together and pushed macrame pins into the ends of the cardboard through the flannel. That was about six years ago and the macrame pins are still there, still holding the cover closed. Works fine.
At one time, I took the cover off to wash and put a layer of thin batting on the cardboard before the cover went back on. That could be glued on. That makes it easier to put a pin into something if needed.
I use this thing a lot, even if it is only about 22 inches square. It goes with me when I need to give a demo, and it sits on my sewing table at a small slant to audition blocks, or just to display something I've made, like a practice block I'm thinking of making more of.....someday? ? ?