electric blanket

 We also got a Kelty 2 person sleeping bag that fits the bed space perfectly, and is good to 20ºF.  Just recently, we added a 5/8th" thick foam sleeping pad along the front wall where lots of cold comes through.  My wife made a cover and we used velcro to hold it on the wall.  Our mattress consists of a 4" dense foam pad with a cotton cover.  The combination of the sleeping bag, the foam sleeping pad on the wall, and the mattress has been plenty to stay nice and toasty down to the low 20's around dawn.  In the morning, I reach up from the bed and turn on the furnace and in about 10 minutes, I'm up in a nice warm trailer making coffee.

We heat our Pod before bedtime and then turn it off. We have really warm bedding for cold nights, and then turn on the heater in the morning if we're not heading out right away. With hookups I use the microwave to heat our coffee water (we're pour-over people) even when we're cooking outside, instead of using propane to heat water. Meaning, same philosophy...we're already paying for the electricity with the campsite fee. 

Good lead, thank you, and I'll keep an eye on Amazon. Because now that you mention it, I also have been heating dishwashing water in the microwave (and then dumping from dishpan into toilet). We already have an extra electric blanket so that's going into RPod too.