The "white board with fuses and breakers" sounds right, but mine is located in the front-most driver's side bay. The chart is hard to read because the print is so small, but you may be able to find it with a flashlight and magnifying glass. The cord reel is operated by 12 volts, so it would likely be the 12V breaker panel the Tiffin guy described. If you find the breaker and it's not tripped, perhaps you can pop open the control switch on the reel to see if 12V is present on it. Could be that the motor's burned out or has a fuse/breaker on it. Here's the G6A Control Panel chart that shows my "cord reel" breaker is #68.
2016 Tiffin Phaeton 36GH
2013 Nissan Xterra S 4WD manual transmission