I home brewed as well, and still teach the occasional friend the ropes. The first guy I lent my stuff to just opened a brewery a couple years ago- maybe I can sucker him into reefing nextThis is similar to something I've been thinking about - thanks for the video!
My previous hobby was (is...?) all-grain brewing. Part of that process is rapidly reducing the temperature of wort (think "pre-fermentation-beer") from boiling down to "cool". To do that, one of the best options was the "Therminator". Would that be an alternative to the titanium heat exchanger, you think? Changes the plumbing a bit, of course, but I don't think significantly so...
Anyway, the therminator is a plate heat exchager, the one I suggested is a tube heat exchanger. there is not a large difference between the two types. The important difference is that the therminator is stainless steel, which will rust in our salt water tanks- a titanium plate heat exchanger would work though. If you have a fresh water tank it would work just fine- although it will probably be more restrictive to flow so I would still go with a tube heat exchanger, just in cheaper stainless steel.