You really should use RV certified units for both, RV CO and LP detectors are designed to operate in a wider range of temperatures and humidity than residential units, they also have a different trip point for alarming. RV certified smoke detectors also have their low battery alarm set to go off when the battery still has more life left in it, as RV's often sit empty for a considerable amount of time, so it is good for them to have more reserve time to chirp low battery for a couple of weeks, vs a residential model which may only chirp for a day or two before going completely dead.
