Another idea I have heard of is to paint (or use decals) some kind of identification on the top of the trailer. Something quickly identifiable from the air, and something nobody (including the thieves) notice right away either.
2017 Escape 5.0 TA (someday soon, I hope
2015 Ford F150 Lariat 3.5L EcoBoost
2009 Escape 19 (previous)
“Most folks are about as happy as they make up their minds to be.” — Abraham Lincoln