Thanks for all the great input. A lot of what was said, we had already planned, ie using electric as much as possible, electric space heaters, etc. When I was a kid, we lived in a 27ft TT for a year while my parents built our house, so I know the heater doesn't work that well. I had planned on using space heaters based on that. I also figure the electric fireplace will help keep the chill off.
So with this new info, I figure if we set aside about $10/month we should be able to fill a tank once a quarter. That's not bad. Again, thanks for the info. I new I could count on everyone here.