If like my '25 5255:
Nothing under the floor of the RV is heated with the exception of the black and gray tanks with heating pads if equipped which I think all BTC's are.
None of the storage areas are heated. The low point drains, fresh water drains, as well as the dump valves are exposed to the elements.
If you're needing to store the BTC in a really cold area, do a really good job of winterizing. I'm fortunate that 1) I live in the south, 2) I run power to the unit 24/7, 3) I run a couple small heaters in the unit when it gets really cold but rare.