This is sort of Dodge Ram specific, but I got out my Fluke meter and checked the seven way plug socket today on my 2016 Ram 1500 diesel. There is 12 volt power always on when the tow vehicle is shut off-even after all the various timers that keep the lights, etc. on after ignition shutoff have shut down.
Why is this important? Because the tow vehicle will continue to provide 12 volt power to the Casita and if enough time passes by, could run down the starting battery on the truck, which would Be A Bad Thing.
So, when stopping for the night or out boondocking, it's best to disconnect the brake and light cable, but it also might be a good idea to put a post-it on the dash to remind you to hook it back up when you get ready to depart. Myself, it's an item on my "pre-flight" walkaround inspection, but your procedures may be different.