We use mechanical birthcontrol devices on our floatplanes to get around this problem. The ones you get at the post office FOC does the trick normally, just scan it for intentional population promotion alterations. That along with silicone and such will keep the worst away from the electronics but water as we all know gets in everywhere if you give it enough time to do so.
There is a special aftermarket spray available now to waterproof speed controllers also, you literally just spray the thing and done and dusted. I don't know if it's locally available but rumours are some varients of it is. You're on your own on this one I'm afraid but a little phoning around should do it.
