RV heating in northern climate?

The temps go down to -50°C here in the coldest months. My furnace is propane. I don't like to rely on fossil fuels though... What could I do to offset or change this? My "handy skills" are low, and my budget is tiny. But I've been looking at gogreensolar and thinking hard about their financing...

We used the window insulation kits that are sold at Walmart or hardware stores.  I haven't looked for them recently but it consist of something like saran wrap the you attach to the window then shrink wrap it to fit with a hair dryer.  This is what I remember may not be the actual directions.

If you have windows that you don't want to see out of you can use the foam sheets that are sold at home depot.  These can be cut to fit the widow.

I have also used thick terry towel over the windows until we could get something else.  We used an electric ceramic heater in the bedroom at night.