You can't expect to be able to sleep comfortably in a moving car. It will be like trying to sleep while someone tries to wake you up - noise and constant erratic movement. Even if you can get over it, to maintain safety you will have to be strapped to the bed and make sure that nothing heavy (even your phone) would struck you in case of an accident.
I once had a great idea - a car that would drive backwards with complicated display system to show a road in the direction you are actually driving. The idea was that it would be safer than seat-belts. But there is a reason why seats (even passenger seats) in a car are front facing. In case of an accident everything will try to maintain it's momentum. If you would have a coffee or a phone in your hand it will struck you in your face.
That's a problem that makes sleeping in comfortable bed inside a car dangerous. You can't get around it for foreseeable future.