I made my own with coroplast (corrugated plastic as used for cheap outdoor signs). Took a sheet ~2" wider than the nook & 2x length + a few extra inches. Folded it in 1/2 & secured with 2 zip-ties. I cover my nook with a small microfiber towel, then slip it into the "envelope" & slip everything into a ziplock freezer bag.
This has been sufficient to protect my STR from the daily abuse of getting bounced around in my fully loaded backpack which I transport in a bike trailer for 3-4 miles before hiking down to my favorite tropical beaches in the rainy season.
Its not particularly fashionable, but does the job better than anything on the market.
Coroplast can be obtained cheap from sign companies...or free along the roadside