http://i1216.photobucket...thouseboat/99d98a56.jpg
http://i1216.photobucket...thouseboat/d0ec816c.jpg
These renderings are of the idea I had about where to locate the hot water heater burner. As you can see the propane locker/tanks are off the stern/transom. The burner itself is OUTSIDE of the superstructure just adjacent to to where the shower is to be located.
The water lines going from the burner to the shower is short (hot water faster.) I added in what could possibly be a build up of fumes (not propane fumes but Carbon Monoxide) during the heating/burning phase of operation. This would only occur during showers and hot water use. I added a flume or chimney to vent possible fumes up/away. The so-called "station wagon effect" of fumes wafting back around into the cabin is the only problem I can see that would make a surveyor red "X" the idea. The burner unit being outside of the structure (preventing build up of gases inside) is the main reason for going this route. Just wanted to run this by everyone to get criticisms/thoughts...hopefully mostly good ones. Thanks, Roger

You might consider:

Mounting the tanks with their tops level with the gunwale - for a better look and to keep leaking propane out of the boat better.

Running the line for the propane entirely on deck, to avoid putting a shutoff solenoid at the tanks.

That, if the windows are closed, there is no fume problem, and if the windows are open, there is plenty of ventilation.

Getting a cap for the stove pipe. Hamilton Marine sells ss stovepipe in 3" but they don't have a cap. The traditional cap swivels to keep the smoke exiting away from the wind.