If it's any warmer than 5 degrees F I don't even turn on the bunk heater, I just use a decent sleeping bag. Although I still set the Webasto engine heater.
To let the truck idle, you must go in to the ECM to change that option. If it is a company truck, you have to have the ECM code. If it was something your company wanted you to do, you would have taken it to their shop. We all understand what you are trying to do, we were hoping the sarcasm would result in a little common sense.