How to Secure Travel Trailer at Campsite?

I stick the ball back in the coupler and lock it. That way both the trailer and ball mount are secured from theft and from accidental dropping if someone lifts the latch. It also provides a place for storage and keeps the greased ball out of the way and clean. If theft is a worry, the most likely parts are the heavy electrical cord, the battery and propane bottles. You can padlock some pedestals to prevent unplugging and turning off the power. Maybe they will still cut the cord, but a well deserved jolt is a good thing. Batteries and propane tanks can be padlocked in various ways.