Not sure you noted it, but it requires some kind of vent else it will just shut down O2 sensor? Using my crappy force 10 cozy cabin heater I find that propane heat (open flame) produces alot of moisture. = not so good in the winter.
Also not sure what you want to do with it? heat the boat, warm some water for a shower, or ?
lastly: you may run into issues at sea, if it is tipped 15+deg (normal sailing), the fireing could be an issue, not sure on this, it depends on the internial design.
but hey, in port with unlimited propane and all of the hatches wide open? I believe you will want all the hatches open to get rid of the moisture.
You might look into one of the webasto type hydronic heaters with a heat exchanger for the domestic hot water, just a thought. I think they use a 1" or 1.25" flue. They cost a bit more.
My opinion: Please: if you do this, get a CO detector just in case. and remember you are betting your life on there O2 sensor. if it fails and you don't have a low 02 warning system. you will fail to.