Welcome to the forum. Does your buddy's Quantum have an inverter? If so, is it turned on? What condition is the coach battery in? If it has an inverter, it's possible the converter may be part of it. Otherwise, it could be anywhere, you'll just have to look in all the bays.
2006 Damon Daybreak 3276 35'with 5 Star Tuner. 3 200 Amp Lithium batteries and 2000 watt PSW inverter/charger. 2013 Elantra on a Master Tow dolly.