It's a popup, not incredibly hard to get out in an emergency, lol. I actually had the Rockwood version of that particular trailer. My wife was freaking out a few years ago when I accidentally locked the keys in ours. She felt kind of silly when I calmly unvelcroed the door and reached in to pick up the keys.
What I'd look into is one of those magnetic door / window alarms. It'd probably only take once of that going off to stop the late night door opening.
2012 Chevy Tahoe LTZ - HD tow package
2017 Rockwood 2703WS Emerald Edition