I'm currently staying in a Carriage Cameo F35SB3 at Tiger Run Resort in Breckenridge, CO for the winter and I thought I'd update everyone with the two cents that I've gained so far. Here's a few things that have worked really well for me:
1) My roof AC has a heat pump option that, when turned to the "on" position, will automatically switch to propane heat when it gets too cold. I've actually found the heat pump to work effectively down to about 10 degrees (fahrenheit). This has been a great way to keep the propane bill down.
2) Open the blinds in the daytime. We have dual-pane windows with day/night shades. When the sun is out, keeping the blinds up lets a lot of warmth in. I had originally planned to insulate the windows with block foam but the day/night shades seem to do a great job of keeping the cold out. They sit about 4 inches away from the windows so it creates a nice air gap.
3) Skirting. Rather than going the block foam route or shelling out a lot of money for a custom canvas skirt (which I'd like to do down the road but just didn't have the funds going into the winter) we duct taped astrofoil insulation around the bottom of the RV and secured the bottom of the astrofoil with a frame made of 2x3 boards. The cost of materials was under $150 and you can get everything you need at Home Depot or Lowe's. I recommend ponying up for residue-free duct tape so you don't leave a sticky mess on your gelcoat when summer comes around.
4) Use DampRid. You can get the little buckets for a few bucks a piece at Lowe's and they last a long time. It's looking like the ones we have are going to last us the whole winter. We've got one in the kitchen area, one in the bathroom, one in the bedroom, and one in every under storage compartment.
5) Get an indoor/outdoor thermometer; it's easy piece of mind. I got a cheap one at WalMart for $10 and put the outdoor sensor in the basement next to my water lines. Right now, it's 7 degrees outside, 46 degrees in the basement and 65 in the coach.
6) Insulate the fresh water line- I ran heat tape along the fresh water line and wrapped it with 3/4" foam pipe insulation. This worked great until temps hit -10 degrees fahrenheit and the line froze. After that, I added a layer of fiberglass insulation around the the foam insulation and haven't had any problems, even when a few nights have gone as low as -30.
7) We've got a 2003 GMC Sierra 2500 Duramax Diesel and haven't needed to use anti-gel. The block heater is needed for a clean start whenever temps are below 20 degrees. There's no need to keep the heater on over night; 30 minutes to an hour in the morning before starting always does the trick.
That's about all I've got for now!