Hi Kevin,
My Espar furnace is diesel or kerosene forced air. In my installation, I will duct the heat into the cabin, through the starboard (left in the picture) side. I'll cut a 3 inch hole through the side of the wall there, and run the duct into the void and forward into the cabin. A fiberglass 'box' will keep the furnace out of the weather, and permit access through a hinged and latched hatch that I 'll add on the face of the box.
If my mould turns out decently, I may be able to make a few copies of the stern box to sell, if there is any interest. But being a perfectionist I'm working at an unbearably slow pace, and the boat is not nearby, adding to the frustration.