If you have the money and you really want to make sure your trailer is where you last left it, I'd go with this one.

But that one is *VERY* pricey. For a cheaper lock option, I'd probably go with something similar to this one. It's aluminum, so that's a negative, but you can put whatever padlock you want on there so you can control the lock quality and key it the way you want it. The Reese lock can be pried off with a crowbar, picked, or shimmed in just a few seconds.