Wintering isn't always as bad as it sounds. Make sure your furnace is sound, first off. Check it well.
I skirt with closed cell foam. Put it really tight under the bellypan and duct tape the seams. Put down throw rugs on the floor to keep the feet warm.
If you're using your water lines, coil the heat tape around them tightly. Better freeze control than just lining the bottom. Don't forget the spigot must be kept warm - anything does that isn't underground. Cover these with insulation and tape the seams. At my winter spot, I also cover the outside water spigot with a waterproof plastic barrel and then cover that with some old quilts. I also have a foam covering for where the hose connects to the trailer.
Everyone loves the bubblefoil insulation. I find it works best if you have it tight up against the glass of the windows. I cut mine to fit just around the glass and hold it in place with painter's tape. Then I put insulation in the trough where the window locks are. I do similar things with the access doors, AC and ceiling vents.
I get a lot of cold air coming in around the door, so I butt the door mat up against it when I'm inside. Neighbors pin up a blanket over their door. I haven't, but bet it would help.
Definitely second the bigger propane tanks.
Good luck and happy camping