Unless Greg...it's super-sensitive to any concentrated forms of particulates, or CO fumes, that could crop up in such a small space as a sealed RV interior?? And, the manufacturer was just playing it super safe (legally) to mention this fact that it shouldn't be used inside that kind of an interior, esp. within the newer fumes you could find in a 2014 FR3 still?
Dunno, sounds like you are okay with the way you are using it tho and are probably safe...people tend to get super paranoid (rightfully so?) about these things not working when asleep? You could also practice redundancy and get a back-up to back up the original...I know, I know...