Looks like zip ties holding it in place -- very practical and "minimalist!"
One thought about zip ties, especially in a bathroom area -- after you clip off the excess "tail," take a piece of sandpaper and smooth out the sharp edges that still remain. It'll avoid accidental skin punctures and cuts when you slide your arm over the zip tie when your eyes are closed and you are reaching around for the soap.
Please don't ask how I learned this trick.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)
Our trips -- pix and textAbout our trailer"A journey of a thousand miles begins with a single list."