at 0 deg F. if you plan on having water in the RV you will need to take extra measures. More insulation, heat trace, RV skirt, heater etc. Lots of people live in their RVs in Montana and the Bakken in ND in the winter.
Most of the newer THs >2008 have larger windows in both the living and the garage. It doesn't matter if its single pain, double pain or triple pain. A lot of heat loss is through the windows. With older TH's <2007 you get smaller and less windows, so that will help, but then again they are typically single pain.
I'd pick out a toyhauler that fits your budget and then plan to make the necessary winterization mods.
As for off hauling it on logging roads, we've hauled both our toyhaulers down Forest Service logging roads, but for short distances. We drive slow.
We have a fireplace in ours. I forget how many BTUs but it puts out enough heat to warm up the main living area to a comfortable temperature.
