The more I think about this, the less I think any of this is going to make a big difference. Winter night time temps reach -10° here fairly often, and sometimes our highs are less than -10° for several days straight. A good battery *will* start a properly maintained, good running car in those temps, IF the car has not been allowed to sit for more than two or three days. 2014 was our second coldest winter on record, with lows reaching -20 or lower multiple times. It was so cold the ground froze to a depth of over 5 feet. I don't buy super cheap or super expensive batteries, but I do try to replace them before they're shot. My Buick never once had a failure to start that winter. But I also drove my Buick nearly every day. My old Saturn did fail, after sitting for three weeks. I think you need to get that engine fired up and warmed up well every day. (I had a 65 mile commute every day plus an hour drive to get my kid on weekends.) The advice about using lighter weight oil is good. I don't think insulating your charger will make any difference. After sitting all night it's likely that it will be just as cold in the cooler as it is inside the car, unless you've got a heat source in the cooler.
One thing you could do - and it would suck - is wake up a couple times and run the car long enough to get it good and warm. That would keep the car battery charged, warm up the interior thereby keeping your backup charger warmer, and help keep the oil from turning into peanut butter at negative temps...
