Again, I would like to caution folks against the thought that all models and all years of an RV will be the same, as it is not true.
In this case the changes can be critical for the results as the 2015 model had a duct to underneath, the 2017 and 2019 do not show that duct!
Then when we get into the 2019, the furnace location has moved from above the floor to underneath and in the back.
Since funraces almost always leak a fair amount of heat, both at the furnace itself and all along the duct run, it is safe to assume the different location and how long and where the duct runs will change how the RV holds temps in cold weather.
If the furnace is mid Rv and above the floor on all the ducts, there will be far less heat reaching the compartments underneath!
Just be aware that every year and every model may have different issues on where the heat goes, so you will be far safer to look at what happens on YOUR RV, not what happens on other RV!
One quick and easy way to get some answers on what you have and where things like water lines and heat ducts are run, is to use the parts catalog!
For the post 2010 models it is an interactive system which is great for drilling down to exact detail like plumbing, so that you can look for where the lines may be run on an outside wall or really far from any heat.
https://catalog3d.winnebagoind.com/menu/Parts.htm
Using an RV in the wanter is often going to be a bit of "risk management" so the more you know about your RV, the better you can make the plans. Sometimes just knowing where the weak points are can help. If you have a pipe in a place where it is likely to freeze, something as simple as parking that end downwind can be the difference in losing a pipe to freezing!