Both my trailers has DC power to the slides, CO2 sensor, and emergency brake-away pull switch 'DIRECT' wired to the battery terminals. My battery disconnect switch is wired between the battery terminal and the 12VDC power dist center on one trailer.
When my DISCONNECT is turned off I still have those three items listed above still connected to the battery terminals.
On my OFF-ROAD TRAILER I have three each battery selector switches setup using BLUE SEA Battery HD Marine quality four-position DC switches where I can select one or all batteries as well as a complete disconnect. Having two battery banks banks it is sometimes necessary for me to be able to be using one bank when camping off the power grid while I am re-charging the other battery bank using my 2KW generator and portable battery charger. My emergency modes requires me to have complete control of all my batteries to be used or disconnected for different modes of operations...
Most folks just have ONE DISCONNECT battery switch to be able to totally disconnect their battery system when in storage mode. It sure beats just operating the disconnect switch instead of removing the battery terminals.
I always thought this was a neat BATTERY SWITCH DISCONNECT setup for the causal user with the removal 'KEY' knob. This could mounted on the plastic battery boxes and looks real neat to me...

Roy Ken