Water tank replacement options
I have two roughly 100 gallon freshwater tanks suspended beneath my side decks on either side of the engine compartment. They are supported on struts to the framing below (it's a steel boat) and there is about two feet of "curved space" below each oblong tank. They are about 18" W x 48" L x 22" H.
The tanks are SS and to judge by the noises they make flexing when full in a seaway, they are unbaffled.
I wish to make new tanks that are fitted to the curve of the hull down low. The boat is currently a tad tender (although I am very much lightly loaded at the moment), and I feel that putting the tanks down low will lower the CG, lower the "slosh" factor, will permit "from above" hose barbs and inspection ports and will free up considerable space above the tanks for large, light things that can stand the warmth from the engine, which will still be a good three feet away on either side. It would also allow a more sensible water fill and manifold set-up and would vent UP instead of the current down into the keel bilge.
My questions are these:
Would it be best to stick with two large SS tanks as is the case now?
Would a set of four or more be better for ballast, "slosh" and cross-containmination issues?
Is there a case for "bladders" of the Plastimo type? If so, how is remaining capacity gauged on such a tank?
Am I missing any obvious tank building materials suitable for a steel boat? What are the best ways to secure tanks firmly and yet isolate them from hard points and corrosion issues? (Once they go in, they aren't going to move unless its' absolutely necessary).
Thanks. I want to do the right thing here.