"Anybody ever drive off with the cord attached?" Yep, several times. I don't like doing it but the heater still works. I now plug in my heater from the box, meaning I ran a extension cord from the front of the truck to the box. I wrapped the 12 ga 25' cord with clear plastic tubing for protection from the elements. Now, when I walk into the garage, I see the cord, and since I have a short garage, I do not have to get out of the truck to plug it in and un-plug it.
I had a long talk with my cousin this weekend who has been working on various brands of diesels for 40 years, and now manages the engine side of large local diesel engine sales/parts shop. I mentioned idle time on a cold engine, and he said that if you are using a good quality oil, (I use Rotella) there should be a more than adequate oil film left on the cylinder/parts to allow for adequate protection even after it's been setting out in the cold for weeks. Just try not to operate a cold engine above 50-75% of MCR (maximum continuous rating) until it has warmed up. He would get in the truck, and after the oil pressure as come up to normal, then drive it to help facilitate oil flow in the engine.
We talked about synthetic oil in a diesel and he did not think (opinion) that it may not be capable of containing enough detergent to adequately meet the needs of a diesel engine considering the inferior quality of American diesel fuel. He thought that maybe in Europe it would work fine.