I use my remote start to get the the truck warmed up.

Sometimes I just suck it up and drive with the heat turned off until I see the temp gauge warm up.

 

I think the block heater is the best way to go, or a nice jacket. But if your going to cover up the radiator i like Lil's idea of the zipper type radiator cover. Cardboard is for packing things, making templates and protecting the garage floor from spray paint, its not an engine component. personally i live in California and can still ride a motorcycle to work most December mornings