In CA its legal with a two way communication device. But after rolling my fith wheel and truck last summer in AZ, Iwill never let any one ride in mine. My two kids and my wife and I came through a little sore, but not much. If we had been in the trailer i dont think we would have survived. The trailer was destroyed and in a huge pile of rubble.
I really don't think it's one of the smarter things to do - temptation is to get up and move around while underway - WAY too easy to fall and get hurt, possible even thru a window. We've traveled with our brother and sister in law in their motorhome, and it requires LOTS of caution just to get up and back to the John - and pretty good balance when you DO get there! :-laf
"HEY, don't worry Mert - I'll clean that up when we get stopped... ":-laf