Be sure the GCFI button in the bathroom is not tripped. Then be sure your 120 volt recepticles will work to run a fan or something that's 120 volt.
Be sure your extension cord is not too small a gauge. If the cord or a plug on the end of the wire gets warm, that's a good indication you need a heavier-gauge extension cord.
The Norcold N512 is a 3-way reefer, that will run on gas, 12 volt DC or 120 volt AC. If your RV battery is low, then when you plug into shore power the battery charger will be going full blast until the battery is somewhat charged. So turn off the reefer, or run it on gas, until you are certain the RV battery is fully charged. Then if nothing else is running on the AC circuits, it should not pop the circuit breaker or GCFI pop-out - unless you actually have a GCFI problem, such as a ground wire not properly grounded, or the bare wire and white wire reversed somewhere in the shore power circuit.
Are you sure you don't have a GCFI problem? I have one shore power circuit that must be wired backwards, because any time I try to use a GCFI something, it pops the GCFI popout.
Grumpy ole man with over 50 years towing experience. Now my heaviest trailer is a 7,000-pound enclosed cargo trailer, RV is a 5,600 pound Skyline Nomad Joey 196S, and my tow vehicle is a 2012 F-150 EcoBoost SuperCrew.