+1 on what John said. If you went with some 180-degree light on the sides of the dump body, that would certainly cover your side warning, but I would still recommend forward & rear facing lights to serve as your primary front/rear warning
I love Whelen, but their rotabeams and V-series surface Mount lights are a overpriced IMO. In this case, I would recommend looking into SoundOff surface Mount intersectors for the sides (they provide approx 180 degree coverage) and I would have forward and rear facing surface Mount soundoff Mpower fascia 4” lightheads. The mpowers are super rugged b/c of their silicone construction (which I think makes them a winner for a dump truck), they’re low profile, and they can be ordered in dual color (amber flashing with steady-burn white for some area/work lighting). You could also scrap the 180-degree intersectors all together and just put some mpowers on the side of the dump too