I don't know if your 12 volt distribution panel is like mine, I had a similar problem with my Dolphin. Turned out to be a loose connection on the interconnect relay. Sometimes had 12 V. sometimes not, tightened the nut no problems since. I even ordered a new battery disconnect relay, before I found the problem.
1999 35 ft. Dolphin 5350, F53, Banks System, 5 Stars Tune, Air Lift Air Bags, Koni Shocks, Blue OX TruCenter, TigerTrak track bars F&R, Roadmaster 1-3/4" rear auxiliary sway bar, 2004 F450 Lariat Pickup 6.0 Diesel Crew Cab DRW, 4X4, GVWR 15,000, Front GAWR 6,000, Rear GAWR 11,000, GCWR 26,000,1994 36ft Avion 5er, GVWR 13,700, 2,740 Pin Weight.