FYI -- My 1" above the cushion PVC railing has worked quite well. The granddaughter was able to get in and out bed quite easily and didn't roll out at night. She didn't get caught is some loose fitting bungee cord and hand herself. I checked with the rules concerning child bed restraints and didn't allow room for the child to slip under the railing.
1. Prevent an inadvertent roll out of bed.
2. Prevent a hanging.
3. Allow easy to get into and out of bed. If something happened that required a fast exit, I want the child to be able to get out. Typically adults sleep at one end of the trailer and the child of children sleep at the other end. There's a stove and furnace
between the two for one thing. Another if one the grandparents had a medical emergency I would want the child to be able to run for help.