You likely have lots of good options as your truck is relatively New.

Here is one type to consider.

Master Tailgate Lock

There are competing brands that are similar. The complaint on these is that many of the components are plastic. The best any security can do is slow a thief down or discourage them enough to move on.

There are also quite a few choices of Locking Tailgate Handles. I would give those extra consideration. They cost quite a bit more, but should be worth it.