Smokey,
We leave the RV heater on, and we have two batteries that we recharge with the generator. However, the kids like the door closed and we get up earlier than they do. I can tell you it gets very cool in there with the door closed.
Right now thre is no solution to get heat into the rear bunk area, just more blankets for the kids. Otherwise, I have to run a new duct to the bunk area from underneath. That means removing the underskin, and a bunch of work for me.
Something that should have been done at the factory (as should the damper in the bathroom)