Not sure how well Duck tape will last. I took small safety pins and took a thin jute string and wove it back and forth thru the safety pins. It is snug as a bug on a rug, But if I need to wash it, I can take it off the insulation board. I find that flannel is easier to keep clean of odds and ends of lint and threads off the design wall with a sticky roller.
I hope to be able to cover the back with some fabric eventually. The 1" insulation is great because you can use straight pins.