As somenone
As someone who used to rep a number of commercial and residential water heaters I really prefer the construction and features of the Iso-temp. IMO it is the nicest boat water heater out there. They even come standard with a tempering valve, something every engine heated water heater should have.
Personally I don't like glass lined steel tanks. It is a cheap way to build a water heater. If I had a $1.00 for every RMA I filled out for glass lined tanks I'd have retired in my 20's....
I know Peggy will disagree with me about the glass lined tanks but I just prefer stainless over mild steel...
The two heaters I like are the Heat Transfer Products "Superstor" or the Iso-Temps.. They are both very well constructed. Heat Transfer Products is a very large and well respected commercial/residential water heater & boiler manufacturer so they have vast experience in building water heaters, I used to sell their products. My mother has had the same Superstor in-direct fired hot water heater in her house now for nearly 28 years.