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I know this is an old topic, but as i did somone else may stumble upon this post too.
I like how this topic kinda trailed off of what the original question was.
Every car I have ever owned I warmed up in the same fashion, idling, didn't matter if it was 11 or -11, I never had a problem.
Electric block heater would be a good idea if you have 110/220v available everywhere you park, and i would not ever recommend forced air heater (110/220v) in the car, unless you want to burn it down.
iv never heard of an insurance company dropping a person who disabled the factory immobilizer, but anything is possible.
this is all i have to contribute.