The cheapest and easiest method of extending your stay is to add nice cozy comforters from home on your beds. You live in NC. The temps at this time of the year can,t be that cool at night. As Mex said, the largest draw is from your furnace. Only use it for a few minutes in the morning to take the coolness off.
Another option is a portable solar panel ,although a bit pricey at first, should be able to top off your battery every day if you are conservative with your electricity and swapped out lighting with LED,s.
Dave
