Home circuit breaker kicks with trailer connected

Are you sure nothing is on? How about your electric water heater? What else is already on this same circuit in your house?
Does this circuit breaker have a little white or yellow button on it indicating it is a GFCI breaker? If so then you may have a ground fault in the trailer you need to find instead of an overload or short.
I would first try plugging into a different outlet, particularly one that is on a different circuit, to see if the problem goes away.