Not sure what your DOT laws are,but watch yourself.If you add a saftey item you may be required to use it.If it didn’t have shoulder belts/harness from the factory I wouln’t bother.
And don’t bother to ask a law enforcement official on the law.They all have the same answer,DUH I don’t know,depends on the persons mood at the time.
Drive like your on a motorcyle and you will be fine.Watch the traffic,turn off the cell,and ALWAYS look ahead for an escape route,And pay attention to how close the car behind you is,and you will be fine.