Jeff Burns, in NTXBG, found this wonderful stuff (3M Scotchkote) years ago and introduced it to the hobby. I seem to recall Been Lee and Rob Wood picking it up from him and trying it out in, what, late 2004? I have used it ever since shortly after Jeff first pointed it out, myself, with great results. Smells bad, is kind of icky, you want to wear gloves when painting it on, as it will stick to your fingers, and looks like a small animal had bowel issues on your circuit board. But it works a champ. Used to be carried at Lowes, in the electrical section. Apparently they have recently dropped it in favor of liquid electrical tape. Scotchkote is NOT the same stuff. You don NOT want liquid electrikecl tape or tool-dip in this application. It will tend to delaminate over time and make things much worse, corrosion wise.
I have a FASST, several Spektrums, a bunch of Hobby Kings. All Scotchkoted. Take the case apart and Scotchkote it, button and all (for safety, bind it first, of course). The button should still work once the scotchkote is dry, Might be a bit stiffish (though I have had no issues). Take care with the servo pins, or carefully scrape the Scotchkote off of them, so you can get a good connection.
Scotchkote the bases and tips of the antennas to and over the insulation to prevent water infiltration.
For servos, Scotchkote the circuit board on the inside, but not the pot or motor (you can coat the motor terminals, of course).
Cheers,