I know we have done it while traveling, but only when really necessary. Keeps me hyper vigilant when driving with anyone back there but I can get on the road at say 0400 and easily clear rush hour traffic while they sleep. Yes we have a CO detector! Wife doesn't like it much but is able to rest. I told her to drive the truck and I would gladly sleep back there, but no! Yes it is legal in CA with two way comms between driver and passengers in trailer. To me that is a walkie-talkie, well that is what we use. It is only ok in a 5er though, bumper pulls are a no-go, at least that is what I read on the CADMV website.
Happy trails,
Billy
