Oh - ok
Maybe a voltage triggered relay is a solution for you. There are fixes one available which turn on at 13.3v and turn off at 12.8 - that's nearly perfect for the rocket. You can connect it directly to the battery (fused) and connect the relay input to the supply. You only need to detach 2 connectors when going to your dealer.
There are also completely configurable ones available - where you can choose both voltages on your own.
When you don't know how to connect it, give me a hint.
Both use a permanent drain off 10mA