Sorry, but if there is NO Black 120 power, then the GFCI will not trip if the short is downstream from the breaker panel. If the CG GFCI trips with the Main RV breakers OFF, the problem is BEFORE the breaker panel in the RV. The fact he has a Surge Guard means he needs to bypass it and then see. I have 34 years as a Tech and have diagnoised (and fixed) dozens of these type issues over the years, and what I posted is the BEST way to determine where the problem is located and to start. A GFCI will NOT trip if it does NOT have Black Hot power. Just having a Neutral and a Ground (and a short/imbalance) will not cause a GFCI to trip. Doug