Our heater is deisel but the idea is about the same.
The heaters are safe provided you follow the
installation manual. You'll need a chimney for it with a proper
deck fitting. I have a cap I attach after I pull out the normal cap. I can't sail with the heater in operation and would suggest you not do that either. They make metal shields to attach to the bulkhead as well as a standoff so the distance is appropriate for the heater. You don't need any
insulation. The shield attaches with small screws.
You want to get a Carbon monoxide detector. That is the real
danger not losing all the oxygen. Carbon monoxide will kill you in your sleep. You do need some source of fresh air but it's not a lot. There needs to be a
draft up the chimney. Your
boat may already have enough venting that you won'yt need it.
Note that when you burn
fuel the proces yeilds cabon dioxide and
water. Imperfect combustion may yield soot and carbon monoxide. No proces is perfect but a well adjusted heater should never smoke. Most heaters take some manual adustment after you get them started. You need to learn how to do this based on the type of
stove.
If you have the specific brand and model perhaps somone here has installed the same unit before.