Way to go Jezza, all in the interest of the diy builders, right? If you design it properly for IP67 then it could be robust for IP67 - let zesc decide for themselves if it’s worthwile.
I find that often people aren’t thinking on diy forums. Buy an esc for 250$, the first thing you do is to put it in an extra enclosure for 50$, cable glands for 20$, connectors for 15$, cables for 10$ and your own time for 200$. To design it into the original design is way cheaper and gives a better result overall. Isn’t this the way you’d like it if you had the choice?
How about those calculations, you on top of it? I do smell that you won’t try since the answer could be the wrong for you.