Why should the outlet be GFI? It isn't outside, by a water source, or in a garage. What other requirement calls for GFI? My 2007 Winnebago Outlook 31C has 3 outlets that are not GFI protected, 4 outlets protected by the GFI at the entrance door, and 2 outlets protected by the GFI on the entertainment center's 400w inverter.
OP, nice job. How about a photo of the inside of the socket mounted on the exterior of the RV? I hope that is a male connecter so you don't have to use a suicide cord.