Hey Tom,
Here's an idea. You could provide Momma with a "contribution" to pay for the electricity you use. I'll bet the electricity is cheaper than the propane.
You wrote: "Currently we are in my mother's driveway and we'll use the furnace if necessary to avoid running up her electric bill. "
I pay Momma (actually mother-in-law) $30 per month for storing a bit of gear and pay my son when I stay at this place and plug in. What am I going to do? leave it for the Federal Govt. to inherit? Ha, Ha ! I'm always looking for an excuse to give Momma a little $$$. She won't take a straight gift but does seems to be content to take the "rent" money for the items in storage in her shed.
Just a thought,
Let's Roll