Rarely do I un-hitch the trailer, unless I do so because we had planned to basecamp... I wouldn't plan to the trip around the trailer. Mine is setup to go anywhere the Cruiser will... though tight trails can be a PITA at times.
When I do leave the trailer at camp, I have a couple of cable locks. I usually try and park it next to a tree or picnic table, etc. Cable the two together and not worry. You can't open the top of my rig without opening the spare tire, and the spare tire is locked, while a determined individual could break in... it will stop the snatch and grab.