Wow. I've got to wonder if you washed out all of the anti-seize during install. You can see it bleeding down the block. Did you clean the hole out before driving the bushing in? I know you didn't dry it out.
Thanks for the support guys.
The red stuff dripping down is threadlocker. There was no anti-seize on the freeze plug. I also dried the hole and roughed it up and the heater with 200 grit sandpaper. Then I used a damp cloth to remove any possible dust and dried it again. I also heated the garage up to 70 degrees.
No, the problem is that I did not drive the heater in far enough. It seemed to bottom out but is was very difficult to apply enough force. If someone is determined to do it I would recommend leveraging against the FEL arm.
The hose heaters are a good idea but I'm a little wary of more surgery. Last winter I added a battery heater so I may just stick with that and a long idle period.