I have had similar issues on my old Bounder. However, looking at the specs for some of the CO/LP detectors, they are really, really tolerant of low voltages. In fact the Safe-T-Alert model can take voltages down to 7 volts and even operate for very short periods down to 1 volt! Can't imagine a 12 volt system getting to 7 volts without everything else in the RV not functioning.
They are sensitive, but I wouldn't ignore them with the furnace running. They may be detecting dust in the system when first started and they also will go into chirp if older than 5 years!
Don't freak, but don't just chalk it up to low voltage either.