I think I would need them to run going down the road. We will be towing for about 8 hours Thanksgiving, and I expect temps to be pretty cold that night (when we will be driving.
I am not sure what the amp draw is on the TV power feed. If I recall correctly it is at max 20 amp, so it would run 2 at the same time. But then if insulated, they should not be running constant, only intermittent.
I have seen some which are dual voltage, but they are about 3x as much money.
Either way - they would only run when either I am on shor power or on the TV.
2013 Coachmen Freedom Express 320BHDS pulled by a 2005 F250 King Ranch CC
A rainy day camping is better than a sunny day at work.