I had a hot wire installed when I had my hitch installed.
FYI: When I had the 12 volt "Charge Line" installed in my Tow Vehicle at Camping World
, they also installed directional diodes in the line.
This allows current to flow only in one direction, to prevent the Trailer from discharging the Tow Vehicle's battery.
There is also a relay system available that is installed in the Tow Vehicle that disconnects the "Charge Line" automatically when the key is removed from the ignition.
Either system allows the Trailer's 7-pin plug to remain connected, and the Trailer's 12 volt systems to be operated, without draining the Tow Vehicle's battery.
I hope this helps.