If you don't have one, you can buy a radiator hose heater at NAPA for $30ish and install it in the lower radiator hose. Its a helluva lot easier to install and its worked fine for me. I see temps in the teens during the winter and the engine has always started pretty easily for me when plugged in.
Or if you want to buy one already assembled from diesel giant, you can do that, although it looks a little pricey:
http://www.dieselgiant.com/diesel_parts_for_sale.htm#Block%20Heater%20Kit