On mine, the ac outlet ground pin is tied to chassis ground.
You can always get a long wire and ground it at a cigarette lighter plug.
Each coach is a little different.
2014 40QBH Phaeton DP Cummins 380HP ISL, Freightliner XC, 2014 Jeep Trailhawk TOAD
Blue Ox Aventa tow bar, SMI Air Force One -South Orange County Ca.