I tried a frost plug heater once. Didn't like the way it worked. Darn thing leaked and I could not stop the leak. I've always used a lower radiator hose heater since that time. Work fine for me.
I installed a frost plug heater in mine. I even made my own sleeve, and I think it took me under an hour. That includes the time it took me to drain and refill the coolant.
Super easy. No leaks. Works great.
Make sure the hole is good and clean before you install the sleeve. Use permatex high temp sleeve retainer.
This will warm the block and the coolant and makes for a nice easy start at -20. Some people complain about the lower rad hose heaters losing too much heat out the rad, but I have no personal experience with them.