I always run a separate 120VAC extension cord into my trailer from the camp ground 20AMP Service receptacle.
This is for my 120VAC Oil Filled heater, vacuum unit, hair dryer, or any other high current unit being used . These units doesn't bother any of my 120VAc units on the camp ground 30AMP Service receptacle...
On my OFF-ROAD POPUP trailer I am thinking about installing an outside flip lid receptacle wired to a more permanent couple of 120VAC receptacle inside the trailer so that I can connect to the camp ground 20AMP Service more conveniently.
Roy Ken