Regarding your concern about CO
The following is an extract from "The carbon Monoxide & gas safety society"
Carbon Monoxide (CO) is a toxic gas which can be emitted from any faulty heating or cooking appliance, petrol generator, or vehicle engine. CO can be emitted from any appliance burning combustible fuel e.g. gas (mains or bottled), solid fuel (coal, wood, etc) petrol, oil, paraffin. CO cannot be sensed using human senses. Special equipment, such as a flue gas analyzer, is needed to test appliances and/or the air in a room for CO. CO can poison in tiny amounts because it is taken up in preference to oxygen by the haemoglobin (the oxygen carrying part) in the blood. Less than 2% of CO in the air can kill in two minutes. Low level exposure of CO over a long period can cause brain and neurological damage.
The key word in this statement is "faulty" because as we all know faulty or badly maintained gas appliances will emit co and therefore kill people.
However if you have the required engineering skills to construct and operate a model marine steam plant then by definition the equipment will be properly maintained and the chances of deadly levels of co being produced would be nil.
If however you don’t have the necessary engineering skills to construct and operate steam-generating equipment then you stand more chance of being killed by gas or pressure explosion rather than exposure to co.
I would strongly suggest that you leave marine steam generation to the competent engineering experts who would not dream of exposing themselves to such basic hazards.