I've been tempted to install an onboard glow driver to one of my planes. The circuit will go like this:
Use a single sub-C NiCad cell; the negative lead will be connected to one of the engine holdown screws. The positive lead will be connected to a mechanical switch and this to the glowplug.

The switch will be mechanically activated by a servo to close the circuit; the servo arm will physically push the switch to the on position and viceversa. This way the circuit is completely isolated from the receiver.

I have not heard of many people doing this, thus I'm afraid there might be some sort of risk to this setup... noise or whatever.

I'd appreciate your comments on the safety of this setup or on how to improve it.