I knew a couple that raced a 36 footer, can't remember the make, and when the water heater quit, they removed it to save weight. Racers, go figure.
Anyway, when my Raritan rotted from the outside-in, it still worked but they used to use a metal case, which was planned obsolesence, and they used to sell a replacement case. Then they started manufacturing plastic cases, but no longer sold replacement parts. I guess that keeps them in business.
I ended up replacing it with a Superstor water heater because I needed a round one to fit the same footprint. The Raritan was very expensive, and I found a distributor in Tiverton, RI that sells the Superstor for a lot less.