I have seen this done a few times online and figured it would be a quick turn around; I was wrong. Every time I think I have it licked, another problem arises. I am at two pumps, one motor, two micro switches and three servos. I do not have batteries or cooling for the motor figured out.
But when I get tired of my scratch builds I go back to this. I did my math and six vessels await my attention plus these two fine examples. Then, I start looking at plans for another one. I may have a problem.

Latest picture is the ballast tank sealed with fittings.