If the inverter has a switch that eliminates any 12V draw, you can install a battery disconnect anywhere you want. Typical inverters behave like that and there are some that automatically do that but are in standby until 120V power is needed.
For your application where assumed storage disconnect is needed, install the disconnect close to the battery. If you choose a master disconnect switch with the right terminals, you can move the CO2 alarm and the slide to the load side of that switch. The only circuit that needs connection to the battery beyond a disconnect switch is the emergency break-away system for braking. Leave that directly connected to the positive polarity terminal of the battery. The reasoning is that even if you hook up and drive away with a battery disconnect switch in the "off" position, your emergency braking system will still operate.
