Yes, the 28BHBE as a 12V plug near the TV, and yes, it's for the antenna booster. It's in the little flip-down cabinet to the right of the stereo (assuming it's still designed the same as our '14 model).
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!