Wood Board Mount
You can take a piece of wood (14 in x 2 in x 1 in) and mount the wood board on the wall using wall brackets, so you can have a flat surface. This is the sturdiest option for grow tent cloth isn’t firm.
Another option, if mounting to the wall isn’t good for your grow setup, is using industrial-grade velcro strips. These velcro strips are perfect for you to use two (2) on the back of your Niwa Grow Hub. You can use it on the wall or even outside of your grow tent. There are many options but make sure to find industrial grade velcro strips that have water-resistant adhesive.