@spasm3 is correct. Having lived in IA and IL all of my life, I'm an expert on cold weather - ugh I really despise it.
Your potable water tank won't freeze if you keep relatively full, but any exposed hoses or pipes are subject to freezing when it's just a few degrees below freezing overnight. At 20F you absolutely want to unhook and drain the potable water hose from the hydrant, else it will freeze and break the fitting on your RV and possibly the hydrant. If there is an outside wash station, see if you can shut it off and drain it, or at least make sure the hose and shower head are drained.
Most RVs use hot air from the furnace to heat areas where there are pipes and hoses on the interior, such as the access area to the plumbing coming to/from the tanks. The key is to run the furnace. If you only run an electric heater, then those areas won't get heat from the furnace and may get cold enough to freeze.
You may also want to leave the doors open a bit under the vanity and kitchen sink to let some warm air into those areas.
The forecast for the next 10 days there shows lows down to 20 and highs between 40 and 55. Warming to well above freezing during the day will prohibit cold soak. When you have an extended period of time that's below freezing, the cold creeps into everything and it can be difficult to keep things from freezing, but with the daytime temps, you'll be fine.
