first off, welcome to iRV2.com. You find a wealth of information and don't be afraid to ask. RV'ers love to help.
Newmar does insulate their coaches well. As well as anyone else. You would have to research back to the 1999 model to find out the specs for that year/model. My two Newmar coaches were a 2002 and now a 2005 model. Mine has R-11 floors and walls and R-14 ceiling. The Kountry Aire is probably higher.
If you can't find anything online, try calling Newmar direct. You can start here Welcome to Newmar Motorhomes & RV | Newmar Corporation
I can say the underbelly is most likely sealed (covered) and insulated so your tanks will be in heated space. In my unit the outside storage cabinet is heated too. Inside was very comfortable when the exterior temp. was down to 0 degrees.
You can also go to the Newmar Owners forum which is part of this site. You may get better information there.