What is wrong with running a 12 amp air conditioner on a 20 amp circuit breaker? I did it for years at the ranch that I lived at. I did have a voltage booster, but that was because I was located about 300' from the main electric meter, and all that distance caused a voltage drop.
Usually you need to carry a 50 to 30 amp adapter, in case you end up in a 30 amp RV park. Then you use the 30 to 15 amp adapter in addition to the 50 to 30 amp adapter to plug in at a house.
I would use the same 50 amp RV cord as normal to plug into the RV, with the twist lock end, then the 50 to 30 adapter on that cord, then the 30 to 15 adapter right at the receptacle.
If you are using a long #12 gauge extension cord, then care must be used if you run the A/C. You could not use the microwave and A/C at the same time, as each use about 12 amps. The battery charger will start out using as much as 4 amps, but will slow to about 1-2 amp range once the battery is full.
TV and other small items normally use less than 1 amp. Refrigerator can be around 3 amps. On a hot day, when you would want to run the A/C, the refrigerator will have more cooling capacity on gas, so I always change mine to gas anyway.
Good luck!
Fred.
