My 1977 300D was pretty whipped. Here was my routine for cold weather. I had no garage
1. extention cord with multiple outlet divider at end near car
2. Timer at wall plug
3. Walmart grade heating pad the kind WITHOUT A TIMER built in
4. old blanket or sweatshirt to wrap battery in
5 convert if not allready to the pencil type glow plugs away from loop filiment
6 electric 200 watt lube oil heater kind with magnetic that sticks to bottom of oil pan.
7. 800 watt block heater
8. Run fully synthetic oil in the car all the time

When it gets real cold I would be accused of "tucking my car in" by the neighbors. Wrap the battery in heating pad, turn it to on. cover with blanket real good. plug in block heater. put magnetic oil heater on bottom of oil pan, plug in. plug everything in and make sure timer is set for at least 4 hours before blast off.

When it is really cold 10 degrees F or less give your self another hour or two or if juice is cheap enough leave in all night.

Remember to unhook everything because I forgot once and well you could imagine the disaster that caused. Hope this helps/Tom