Actually, the SS tank is heavy gauge and still in excellent condition. From what I have seen, the quality is better than what you can buy these days for under $800; just need to keep an eye on the element mounting plate which is galvanized steel. I fully expect this tank to out live me, and possibly the boat as well.
Take note of the copper plumbing nightmare I had to deal with. Undoubtedly, a new tank of any kind would have to be re-plumbed to match all these fittings - no simple job in itself with only 3 feet of ER clearance.
To the degree that I can, and where it makes good sense, I like to know as much about my boat systems as I can. I do not just consider my water heater as a "black box" to be replaced like a microwave oven. I also took the rebuild as an opportunity to reduce the element size from 1500W to 1200W so it would not take as big a bite out of my 30A dock supply.
And, yes it connects to the engine hot water, but had not been re-plumbed for that at the time of this picture. I need to get back and take some final shots now that everything is reconnected.