[JRTJH]

Yes, it works by creating a "feedback circuit" in the trailer. The converter will form a "continuous loop" that will be "charging the battery while drawing power from the battery" so the converter circuit breaker needs to be turned off.

The problem, one that can be deadly, is the male end has 120 VAC on the pins. Anyone who might unexpectedly unplug that extension cord could be electrocuted. Even if the "adults around the camper" are smart enough not to do it, the visiting toddler that happens to be following a butterfly into the passthrough could be killed by that type of "inappropriate electrical modification"...

I'd advise that if you're going to do it, just run the extension cord (with a male end and a female end) under the trailer and plug it into the shore power receptacle on the trailer. It's safer, prevents an electrical hazard and you still need to turn off the converter.