On many electric planes the servos are mounted with no rubber isolation between the airframe and the servo. On electric planes it's usually not needed to have the servos isolated because there is little to no vibration from an electric motor.Infact, many ofthe major manufacturers will recommend directly mounting the servos to theairframe with no isolation. The attached picture is from the Electrifly SPAD XIII park flyer.As you can see in the picture, the servos are mounted directly to the wood of the airframe. I have this plane and have well over a hundred flights on it and have had zero servo problems.

If your plane is glow or gas powered then the rubber isolation mounts are absolutely necessary and leaving them out will result in servo failure. But if you have an electric you can usually get by without them.

Ken