I have a CO detector on board.
I thought I would put metal plates over two burners, and a vent from the third. The heat should be conveyed through the sides and top of the oven, and the plates, even the stack. I have found that using the oven warms the cabin. I don't plan to use this for freezing temps, just the occasional cool night. What kind of oven were you using? How did you vent it? I figured maybe 3" pipe.
Sounds like a clay pot might do the trick for occasional cool nights.
My design was based on heat exchangers that transferred heat to air which is all it would really be. I had the whole top of the stove, encased. Mine is square, steel and easy to cover. Thick aluminum plates would be across the top of each burner a several inches above the flame (actual distance and flame setting would be determined in testing). The plates would angle up toward the middle so the hot exhaust gases would rise and combine then hit other plates which would direct the gases through a 3" insulated duct to the portlight or the hatch directly above.
The main part would look like a box about 12” high sitting on the top of the stove. Most of it would be made of flat bar aluminum including fins on the outside over which fans would blow cabin air. I think I would end up using a heat shield so people could fall against it or grab it for support and to direct the heat to the center of the cabin.
A fun project that can be done with basic tools but not one I wanted to do on the boat though I still think about it. The advantages were cost. A few hundred dollars buys a lot of scrap flat bar (none of the pieces are longer than 2’), it uses outside air for combustion air, exhausts through an already existing hole in the deck and can break down for storage. It also collected water, not that I would drink it.
But still not as nice as Hydronic. Hydronic is crazy expensive and much harder to install than making a heat exchanger for the stove but it is push button easy to use and doesn’t preclude having coffee in the morning!