Windy conditions blowing against side of RV when WH is located.
Window was cracked open and CO alarm in bedroom went off
Aired out RV....closed window near WH ...no more alarm
Water heater combustion/exhaust chambers are submerged in water so only exhaust fumes exiting can be pulled back inside the RV
Furnaces.....heat exchanger pressurized and if cracked fumes can be blown inside RV via floor registers
Fridge less likely due to Fridge top/bottom/sidewalls sealed and flue is directed upward
*Course that is IF RV MFG installed it correctly