I'll check my DOT book when I get home But I know on big trucks anything wider than the cab has to have marker lights on it with a reflective lens or tape at each corner.
so on the back of a deck a reflector should work i have no location for a light? i cant make heads or tails of this metric crap lets talk inches, like who ownsa metric tape? do they make such a thing lol.
Anything over 80" wide needs two front yellow marker lights on the outside of the deck. On the rear you should have four red lights two facing the outside and two facing the rear also three red in the middle of the deck. If the clearance lights don't have the refractors incorporated in them you need to add reflectors.