Questions on battery setup for enclosed cargo trailer

And like Bedlam said, if you want power in the trailer when it’s not hooked to the truck, it is not difficult to setup. And not horribly expensive.
Just make sure your expectations are in line with your setup.
Just for lights, if I’m at home, I have a drop cord run to the trailer for a work light, or fan/heat to keep the trailer and toys dry.
If I’m on the road anywhere, it’s likely hooked to the truck so the interior lights work off the truck battery.