About all you can do is make it difficult for the thieves. They will get your battery no matter what you do...
My trailers are in spot where the back house lights comes on from movement in the back yard.
Putting your batteries is a locked steel box is what most folks do. The keyed side latch is the better lock as just using a regular lock can be cut off in seconds.
As always out of sight out of mind is best defense I think...
When you get your Honda Generator don't even think about leaving it abandoned along with the trailer. Keep it locked up in the bed of your truck and covered with a locked folding bed cover. My 2KW Honda goes where I go...
I have even thought about a motion detector operated fence shocker unit. But I would be the one to go to JAIL probably for harming the thief.
Roy Ken