You can do it either way, totally your choice. But you need to make sure you've disconnected the battery so you're not draining it due to parasitic draws. Many, if not most, factory battery disconnects don't completely disconnect the batter from things like radios, lights, and various other devices. A couple of weeks, or less, will give you a dead battery.
I spent $30 on a 10 watt solar maintainer since I don't have electric where I store the trailer, and didn't want to pull the battery. I've checked it a couple times and it seems to be doing the job.