Check this out.
http://www.nelsonhobby.com/advanced_glow_switch.php
I have been using these for many years now. I have never had a problem with the battery life as it only comes on if the plug starts to cool. Never lost an engine when using this device. You would need a single cylinder model and a twin cylinder model. While I have never had a 3 cylinder engine I have used both the one and two cylinder units and both worked as claimed.
Fred

As I recall, mentioned on the web site is that for more than two plugs additional units may be used. An email or phone call to the vendor would answer your questions.
I would not use my RX pack for anything but my RX.
Fred