Hi ntonca,
Welcome to the Heartland Owners Forum and to the family. We have a great bunch of people here with lots of information and all willing to share their knowledge if needed.
Your furnace will have an open duct into the enclosed underbelly. So the only time it is heated is when the furnace is running. If you plan on camping in some really cold weather for long periods of time, you may need other things or need to look under your unit to make sure everything is insulated good and water lines not touching metal.
I'm sure we will get some more and better answers from other North Trail owners also.
Also when you go for your PDI,,, do a really good check over... slow,,, make sure everything works,,, you can work everything... have them hook up water and put water in tanks and watch it drain. And if possible,, stay overnight at the dealer or close by and check it out.
Enjoy the forum and your new toy.
Jim M