Which Manufacturers make a true 4 season class A ?

That depends on the owners and what they consider comfortable. We leave Florida most every Winter and head out West into the mountains and snow. We don't have any need for 70 degree temps inside at all times and it is not unusual for us to have upper 50's lower 60's in the mornings. The dog loves the cold and we have an electric blanket. When we travel in the Summer, we have AC, which is more than sufficient. We could run the furnace a lot more, but see no reason to. We do have dual pane windows, but as everyone knows, the biggest window of all is your SINGLE pane windshield. We have an insulated wet compartment but we do put a 100 watt bulb in it when the temps are going to be approaching zero. Never had anything freeze up since we only hook up our fresh water or sewer hoses to fill or empty the tanks.