There are other things on when plugged into shore power ( convertor charging battery, Co detector, fridge and furnace control boards). In addition, when the AC starts after the initial start it usually had a pressure head ( remaining from last run) that the compressor has to overcome. This causes a higher than normal current draw. You should be OK at the 20A site if you do not run the AC and manage the other larger appliances.
2015 Freedom Express 248RBS
TV 2015 Silverado HD2500 Duramax
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2 65W solar panels