When we resurrected our 64 Safari. I installed a Twin Temp Junior from Precision Temp. It does both hydronic space heat and (on demand hot water). It is fantastic in both regards. The wife likes long showers, or baths and we have never ran out of hot water. Great for booney camping also. Shermantic, For your application Precision Temp also has stand alone (on demand) tankless water heating systems that are either floor vented or wall vented units. URL, PrecisionTemp - Tankless Hot Water and Heaters for RVs, Boats and More
. I hear Aqua Hot is also a very good product and Atwood has been around for a long time. I suggest doing some research. Precision Temp is made in the US and there customer service is great. I had a question on a Sunday so I called and left a VM and got a call back in 10 minutes, by the design engineer. Who does that now days? Best of luck with your search.