Using propane for heating makes a huge difference. The furnace will use an enormous amount of propane while simply cooking, heating water, and running the fridge is minimal. We (2 adults) are usually living in our motor home from 7 to 10 months each year. during that time I usually only fill propane once. I have a 30 gallon tank. I try to stay in rather warm places so I use very little furnace heat, relying mostly on my heat pumps and ceramic space heaters.
Water usage is another matter entirely. With normal use, i.e. two showers every day, two loads of dishes, flushing toilet etc. we can usually go for 3-5 days without dumping the gray tank. Understand this is NOT trying to conserve very much. If we have to focus on conserving tank space or fresh water usage we can stretch that to 6 or 7 days.
I have never lived in Illinois but I have spent winters in Kentucky,