From what I've seen, hitch locks don't help much. Some thieves have methods to get around it (smaller hitch ball, just use the safety chains, etc.) That is why I use stout wheel locks.
On a different thread, I asked a similar question because I'm looking at buying an enclosed cargo trailer for additional storage when dry camping, and it would be stored in the city proper (thus issues about break-ins). The parking enforcement boots mentioned above are pretty sturdy, although anything will open to a cordless angle grinder.
My take is that I have insurance on the trailer. However, I'm going to make a thief fight for it so there is one less meth lab in central Texas. Brinks "J" locks were pointed out (as I mentioned earlier), with the included crappy disk lock tossed and a genuine Abus one put on. If I am concerned that isn't enough, I'll spend the 300 bones and go with the Sold Secure Gold "winter wheels". Any thief who manages to steal a trailer after getting those off is desperate enough that nothing will stop them anyway.