The company I work for actually manufactures Carbon Monoxide detectors. While the style we manufacture are designed to be connected to a burglar or fire alarm system, I can offer a couple of things that come to mind.
First, as mentioned, Carbon Monoxide detectors and alarms have a very limited life, but the life-span is actually closer to 5 years, with many having a useful life of only 2-3 years, so please be cautious in that regard, and make sure to take note of the expiration date that will be located on the device (this date is required to be on the device, so if you don't see an expiration date on your detector, it's time to buy a new one).
Also, carbon monoxide detectors have limitations with regards to temperature and humidity. Just like smoke detectors, you can expect the devices to operate in a temperature range of around 32-104 degrees Fahrenheit. For this reason, I would probably recommend a new CO alarm each year (after the winter in the north, and after the summer in the south), as most campers are not kept in a temperature controlled environment year-round.
As for power supply, either way will work as well as the other, though I would recommend something with a battery back-up at a minimum.
For the most part, I would feel very confident in installing any manufacturers CO alarm or detector in my camper. The truth is, the detectors are being subjected to environments outside of their operating range, so device degradation increases exponentially.
Yes, even for the kind I sell
Just my thoughts. Hope the suggestions help keep everyone safe...
Greg and Robin
2013 Dodge Durango
Sent from my iPhone using Fiberglass RV