The white wire looks to be your negative lead.
The black and the red are both positive leads, one likely goes to your power tongue jack directly and the other is your main 12V hot lead to the power distribution center inside the camper. Your CO detector is connected to that power distribution center along with all your other 12V accessories. The power distribution center also handles your 120V needs when hooked up to shore power (30amp hookup)
For battery disconnects I like the Blue Sea m-series
made for boating applications