We've had to do that when it unexpectedly rains during a race. We've used plastic grocery bags and poked a hole in them for the antennas.
At a race, one of the racers knocked his transmitter off the drivers stand into the water. It was submerged for maybe 20 minutes until it was found. He did nothing, let the water drain out and it still worked! I don't advise trying that stunt though.