Bruce,
Your 1st post "logic" is the same way my steps functioned when new
To stop the steps coming out we have a frig magnet handy that I stick to the door switch (actually to the wall very close the switch) - it completely stops the steps from coming out. The system thinks the door is closed.
Itasca / Winni wired mine
Door switch power from ignition switch and main power from the Engine battery before the disconnect solenoid. The disconnect switch had no effect on the operation of the steps. The Engine battery always had a unwanted drain.
I changed the wiring by moving the main power to the house batteries after the disconnect switch leaving alone the ignition switch connection. Turn off the house batteries and the steps do not function. Nice when getting access to the batteries which are located inside under the stairs
We always dry camp with solar charging the house batteries
No need for an extra load on the engine battery which is most of the time isolated from the House battery bank
The step lamp and the motor plus a small parasitic load from the controller were draining the engine battery unnecessarily