IF it is only having Electrical issues when on a 20A outlet....suspect that 20A is GFCI protected and one of the heater elements
Turn Off ALL Individual Circuit Breakers in the RV AC Power Panel
Then plug in/reset that 20A Circuit Breaker
If it Trips....turn off Both 50A CBs in RV AC Panel and try again
If it trips...problem is Adapter(s), RV power Cord,
If it Doesn't trip witn RV 50A CBs closed...close each Individual CBs One at a time until the 20A CB trips....then ID that circuit and check it for loose wiring/bad connections etc