Cleaning with alcohol helps absorb water from the circuit board (you need to open the Rx case of course). Subsequent to that, spray the circuit board with WD40 to help prevent future corrosion. With regards to the ballon, squirt a bit of RTV into the ballon end where the wires come out so water can't enter there.

Funny, but I wonder if a person was to "T" the exhaust pressure line (on a nitro) and feed a line into the ballon. Keeping it pressurized would keep out water in the event of a pinhole. It's only about 1 psi, so the ballon wouldn't inflate much, just swell up a bit.......................er.....nah,, silly idea....LOL.