I finished the design wall today.
I attached it to the wall with Velcro Dots, mainly at top, it took only 5 dots per each 4x8 1/2" insulation board.
I ordered the extra wide flannel at Dharma Catalog to cover the wall without a seam.
I started hanging the flannel by pivoting the insulation board out slightly from the wall and T-Pinning in position on top. I left a 1" or so to pin just behind the insulation, tucking as I pinned.
After I got the top of the first board pinned, I went along the side, tucking and pinning, then slid the insulation back into position. I continued along the top of the next board, pinning and tucking and then down the other side. I had excess along that side that I ripped off without pulling on the flannel too much. I also pulled the flannel taut as I pinned and tucked the remaining side. I pushed that insulation back into position.
Just to be on the 'safe' side I hammered just 4 larger T-pins into the wall along the top of the insulation board.
I have 3 electric switches & an outlet that I had cut out of the insulation. To access this, I pierced the flannel and
trimmed it away, leaving a 1/2" to pin down around the opening. Not too bad.
It was a'job' to handle a big piece of flannel and I wasn't sure it would work but I now have a 8'x8' design wall!