I think you might be better off with a coolant hose heater. They are cheaper, easier to install and do the same thing. It works by convection, you install it in the lower radiator hose and when you plug it in the coolant near it heats up and naturally rises to the top of the radiator. At the same time cold coolant moves into it's place and it keeps cycling.
I have never needed to use my coolant hose heater. I snowblowed one day while it was 6 degrees below 0 (-6 degrees). What I do is let the glow plugs cycle and start it and then immediatley turn the key back to the glow plug position for a couple of seconds until the rpms raise up to a good idle.
You are not draining your battery since the engine is running when you turn the key to the glowplugs like you do when you just cycle the plugs twice before starting. This works like a charm everytime.