Again I'll say go with dual pane windows and in floor heat if you find it. DW and I have lived in an RV six months out of the year for the last six years. We find ourselves in cold climates in the spring and fall before heading south for the winter. Our home base winters are -40f to sometimes as low as -60f (Alaska can't be that much worst.)
What most are stating are the RV spec's because that is what they know best. What I'm trying to tell you is it's all about the comfort level when you're living long term in your rig.
Those RV furnaces are inefficient and will only warm the rig from the knees on up unless you really crank them up. Even then the heat will not be evenly ducted throughout the rig. Electric heaters in key living areas are only good if you have power to run them.
The difference between single pane and dual pane windows is an R1 to about an R4 (not much,) but it will greatly reduce on the condensation within your living area. You will have enough of that with the windshield alone on a Class A. Most Class A's are not laid out well to have a dehumidifier just sitting in a corner.
Yes the aluminum around the windows will be cold and sweat, but there is no other option like in a house. BTW, you'll need to keep an eye on those window tracks for mold when buying used. A lot of older RV'ers with failing eyesight and mobility will let these area go. If there's mold there, there could be mold elsewhere. I've seen several that will suffer from an allergy flair up once they get on the road and are living full time in the rig.