[Festus2]

The "Arctic", "Polar", "Thermal" label that Keystone applies to many of its RV's is an advertising gimmick that gives the impression that your unit will be able to withstand freezing temperatures. There have been numerous threads and discussions on here about this topic which you may want to research using our forum search feature.
Briefly,........
1) You cannot leave your unit for long periods of time in freezing temperatures unless you have taken some preventative measures to avoid having your lines freeze up on you.
2) The "heated" underbelly only provides heat when your furnace is operating. The amount of "warmth" it provides is, at best, minimal.
3) The large, uninsulated air space in the underbelly has many openings which will allow cold air into this area.
3) If you cannot supply supplemental heat to the areas where your plumbing/water lines go through, then you should drain the lines if the unit will be left unattended or not used.
4) How cold can I use it? Depends on the temperatures you are talking about. If the temps drop to slightly below freezing, you can use it as long as your furnace will supply enough heat to keep you comfortable or you are plugged in and can use space heaters or something similar.
5) If you drain your lines, you can always take bottled or plastic water containers with you. If you drain your lines and your HW tank, don't try to heat the empty tank with propane or electricity!
6) Eventually, you will have to completely winterize your TT and fill the lines with RV antifreeze. Google "Winterizing an RV" and you will find plenty of info about that online.
7) You can still use a partially or completely winterized RV except that you will not be able to use any water.

Again, don't be mislead by these labels from Keystone. I would bet that no one from there has ever slept in freezing temps in one of their Polar/Arctic?Thermal packaged units!

Hope this helps.