Pick out a color for your balloon cover that you like. I use different colors for each servo and the receiver. I like to have color on the chassis and this is a good way to make yours stand out. You may want to have matching colors and we all know that blue is faster then any other color...
Carefully stretch the balloon over the servo (or receiver) slowly working from the end that doesn't have the wire sticking our of it. It can be tough to get the balloon over the servo but if you stretched the balloon before you started, it makes it easier.
Work it over the servo little by little. Take your time or you can break the balloon. Once you have done a couple of them you will get the hang of it and each one will become easier to do. If you do happen to break one of the balloons, don't worry as they are inexpensive and you have a bag full of them.
Once you have the balloon completely over the servo, the wires should be sticking out of the balloon as shown. You now need to punch a hole where the servo shaft is with a pin. Once you have the hole you can easily work it around the servo shaft so it sticks out of the balloon. Do not make this hole very big, just use a pin to make it. By stretching it out over the shaft you make a nice tight seal to keep out water and fuel. By using a 9" round balloon on a standard sized servo you can see that it fits nice and tight around the servo. This size also works nicely around standard sized receiver, if your are using a smaller receiver then what is standard then you may need to use a 7" balloon to make it tight.
Just use a tie-wrap or twist-tie to around the neck of the balloon to seal where the wires exit the balloon. Here you see the completed servo. The balloon is nice and tight around the servo making it easy to install. The balloon is also snug against the output shaft and there is a tie-wrap around the wires to keep any moisture or fuel from entering there.
It's now time to install the servo in our vehicle.