There have been cases people have described where you can end-up getting CO from being in a marina surrounded by other BIG boats with their generators running.

Diesel generators and engines don't produce as much CO as gasoline models. Propane and other heater are more problematic. Instant hot water heaters are more of an issue to be concerned with.

We've had CO detectors hard wired into our 12v system on our prior and current boats. We had a diesel central air system (Expar) on both our prior and current boats. We have a generator on our current boat. Our CO detectors show not only the current level, but supposedly accumulate the aggragate levels. (You can have a smaller threshold current level, but be overcome by long-term exposure vs. a "surge" load...) I'm not sure these are marketed anymore.

Anyway, it's pretty cheap insurance.

P.S. - the 12V RV models are about 1/2 the price that the "marine" models that I saw from West and Defender. There were current models in the below $60 each range.

We put them in the main and each sleeping compartment.

They draw very little load -- unless the alalrm is screaming at you ;^)))).