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
Does anyone use this idea in your truck conversion?
"I have marveled often at the thin line that divides success from failure and the sudden turn that leads from apparently certain disaster to comparative safety." Ernest Shackleton, Antarctic Explorer, Sea and Land, 1874-1922.