We winter in Indiana in our 3400RL and here is our preperations.
We bought removable vinyl skirting here:
http://www.ezsnapdirect.com/products/rv-skirting if you are only going to be in the cold one season you might want to just use the foam board you can get at Lowes, Home depot etc. but you do want to skirt the bottom, it helps a bunch.
We bought a heated hose here:
http://www.pirithose.com/ these work great and are safe for drinking water. You can also buy a heat tape at the hardware store in various lengths, use electrical tape to hold it onto your hose and then cover the entire hose with the foam 4' insulation tubes from Lowes (Home Depot, Menards etc). Just plug it in and the water stays flowing. We do let the faucet dribble a small stream when the temps drop below zero overnight just to be safe.
I use a 3" PVC pipe in place of my slinky type sewer hose. This way I can keep the sewer pipe at an angle so it drains good. I leave my grey tanks open all winter and drain the black as needed. You can use the slinky hose but make sure you have a straight run with a decent angle or the "water" could pool in the hose and freeze.
I bought a cheap battery operated remote wireless thermometer at Walmart and mounted it in the convienance center by the water hook ups. I mounted the read out for it inside the 5th wheel so I can moniter the temp. in the basement.
I also ran an extension cord from the campground post into the basement using an adapter onto the 30 amp plug on the post. I plugged a small ceremic heater into this cord and sat it into the laundry basket that we access with the hatch in the hall way. I keep the thermostat on it fairly low so it would only come on if the basement temp dropped below 50 or so. This was just a safety measure to avoid any freezing problems.
We have a space heater in the living room and another in the bedroom and use these to help out the furnace when needed.
Last winter during the coldest weeks we went through about 100lbs of LP every 10 days or so. We did have a seperate 100lb tank. I hooked it up by buying a seperate hose at camping world and hooking that up to our on board LP regulator in place of one of the 30lb tanks. I also installed one of these:
http://www.pplmotorhomes.com/parts/l...ator-valve.htm it lights up when the regulator switches LP tanks so you know when one tank is empty and needs refilled.
Last winter we had no freeze ups and were pretty comfortable all winter long. Hope this helps you some.