[Al Skierkiewicz]

Fredi,
At high current, I would be concerned with expansion and contraction coefficients of the material and the electrical components. I think the epoxy can do a great job as a heatsink when exposed to water. What I might suggest is a double dip such that the tabs of the transistors only are embedded in the epoxy while the circuitry remains open. Then encase the assembly as you have shown. This would allow the components on the board to move around with temperature without being broken off as material expands and contracts. I like the dual heatshrink and would recommend it for the entire length of wire. Some wire insulation is made with clay as a filler and therefore it absorbs water. Some wire has a dual coating to prevent this as well. As a test, seal both ends of a short piece of wire and submerge it for a day or two. Then slit the wire open and see if there is any contamination. If you heat the shrinkable tubing and then compress while hot with pliers, the seal should be good enough to keep out water.
As always, I applaud your team. This is a great idea and a wonderful demo. Good Luck this year!