If you are considering a 5th wheel, the answer is simply....Yes! But, they are rare, heavy, and expensive. “IMO”, 4-season includes extended use at or below 0F. My opinion again....if the unit can’t handle that....it ain’t 4-season. Prior to the last big recession, there where several manufacturers that produced true 4-season units designed for full time use. However, most went under, as the market could not support them. If you’re willing to buy used,there are many on the market, to be had for much less than the original sale price. But, as with anything used....buyer be “AWARE”! You must thoroughly inspect the unit!
We had a previous 5th wheel, that we full timed in....seeing several morning temps at -30 F ( or slightly cooler), with no issues. With our present unit.....we wouldn’t hesitate to use at a -20 F or cooler with all amenities in service! But, you will use a lot of propane, when the temps stay at or below single digit F!