They are used on sailboats to keep the person from rolling off the bunk/berth/sleeper onto the floor as the boat heels over. In hot climates, mesh or netting is used to improve air circulation.

They look like this

https://picasaweb.google.com/todd.huss/20071024MorroBayT...#5125149809406594034

Does anyone use this idea in your truck conversion?

......Every bunk has to come with a safety net[FVSS REQUIREMENT].....using it is another issue.....I'd suggest on the top bunk at a minimum.....it is the law for commercial Drivers.....[ALSO KEEPS THE FAT GIRLS FORM KILLING YOU IN A CRASH]....ooops didn't mean to say that about my tractor and some of the girlz these days........sorry if I offend any fat chicks!....geofkaye