Waterproofing your electronics  The hands down best solution is to use a conformal coating (How to), it will completely seal the part preventing any water from reaching the electronics. It dries hard like an epoxy which is what it really is. When its completely cured cover the part with shrink-wrap to protect the coating. The most popular product is 3M DP-270 clear, I've been told not use the black material only the clear.When coating your equipment you want to make sure not to cover heat sinks or the metal tabs of your ESC Fets. This is because the covering is also and excellent thermal insulator, so leave the parts that need to be cooled uncovered and exposed to air.  Also make sure all the plugs you use are plugged in when applying the conformal coating. Any contacts you want access to later on need to be covered with tape so that the conformal coating wont cover them. When you do break the coating by unplugging a plug, just reapply some after replacing the plug.
With this method you can dunk an Rx or ESC under water and still run them reliably. Of course find this out the correct way, after one of those unexpected issues. Easy Waterproofing  Although not as good as a conformal epoxy coating method which completely seals the parts, a good easy alternative is to use Aeroplate which is a dielectric lubricant.
Aeroplate has an oil like viscosity and it effectively displaces water plus its dielectric ability allows current to flow uninterrupted. I have put this to the upside down soak test and everything worked great both while wet and when dried out. Aeroplate is another name for CorrosionX and the Stuph. Give it a try on your ESC, Receiver and servo, it really works! One tip, don't get the oil where you want to apply any adhesive tape or double sided tape, etc. This stuff seems to attack these adhesives so they don't bond to surfaces, thoroughly clean these surfaces. Water up your tube! There are quite a few theory's as to why water works its way up the stuffing tube and into your boat (ranging from pressure differential to pumping action of the flex spiral), but putting aside why it happens fact is that it does. Two things that you should do, first chamfer the back of the drive dog so its not a sharp edge. This has been shown to help in some instances.
Another thing to do is use a short piece of silicone tubing over the end of the stuffing tube. You want to leave enough of the tubing extending over the tube so it closes down to the flex cable size. You want it to gently touch the flex cable, just enough to keep water out. | 
