Hallo Bobby,

may be that we are trying to solve the problem at the wrong end?
What do you think about the use of special high efficient 12V motor like they are used in model racing cars or boats? They could be controlled with PWM to decrease supply current and heat dissipation. At shaft drive there could be mounted an additional pump mechanics. By making an metallic enclosure arround it, only having leaving electrical cables and both tubes, it could be made waterproof and cooling power dissipation (for avoiding that ship is burning or smelting). Choosing the right components you can make it room saving, just for your needs.
You can also have motor and pump seperated by using a flexible shaft drive.

Special high effiecient motors use certain magnetic material with increased induction and certain high precision fabrication technology (very small air gap) for achieving very high revolutions. Effiency of such motors can be greater than 90%, when I remember correctly. And weight saving is enormously, which could be advantegous for you, right?
For the pump, I know that there are also weight saving mechanics made of special synthetic, fibrous material.


Bye,
Kai