Francesca: ....like a long piece of lumber or I-beam extending beyond the tailgate of your pick-up requiring a marker attached, ANYTHING sitting in/on/under any vehicle making it 80 inches or more wide will require some manner of safety lighting or passive reflective marker at some level of government (Municipal, State, perhaps even Federal, or maybe all three).
The question is: IF someone hits you, or, you hit someone else with your 80+ inch wide motorized vehicle on some public road somewhere, do you want to take a chance (think: potentially catastrophic liability; or ruined conscience if a cyclist or pedestrian slams into some part of that 80 inches at night, while you are underway, stopped at a light,or, backing out of a parking locale) ?