Short in house wiring

Hello, I own a 99 Damon Ultrasport 36' single slide my. I am battling a short in the house wiring. The short is in the GFI circuit. There are 6 outlets on the GFI circuit. I have a 20 year master rv tech working on it. He has pulled every outlet and still the short is there. My tech said that after looking at the wiring at each outlet that there has to be a junction somewhere but he can't find it. I tried calling both Damon and Freightliner to try and get a wiring diagram but no help. Can anyone out there give me any direction. My tech is in this about 6 hours now. He is talking about dropping the belly pan and running new wire! Any thoughts or wiring diagrams would be appreciated. Thank you, Lee