I went camping at Murphys Creek Escape on my own whilst I had to attend Uni for a week. I pulled up at the site, reefed on the handbrake, unhitched the trailer and moved the car forward about a metre. Got out of the car looking at my feet as you do and looked up to see said trailer rolling down the hill. Five massive strides and I was able to turn the trailer sideways which stopped it's forward momentum. Just as it came to a stop, old mate that was sprinting down the road pulled up and says "that was close". Another two metres and the slope got quiet steep, another 5 or so metres and it was over the bank of the river, down maybe 10 metres and into the drink. Checked said handbrake, could quiet easily turn the wheel even with the handbrake pulled tight. I have since adjusted the handbrake (Murphys Creek was only my second trip out in it!) but i now also chock with timber, just in case.
Robbo