LGD Owners - Would you be concerned if...

We have our little 4-month-old Max who is a super little dog.  He stays outside all the time except for 'visits' when we bring him inside the house to play for a short time or take him for a ride in the car.  Well, he never complains at all outside - no whining, no crying, no barking unless something or someone strang is seen.  But, tonight it's going down to 18 degrees F here in Oklahoma and I'm a little concerned about him.  He has a dog house with a flap over the door so it's not airtight, but it's close.  There is no heat inside it however.  I'm wondering if just the little guy's body heat is enough to keep him warm. 

Oh, he is half Anatolian or Saint Bernard and half Great Pyrenees.  He weighs about 35 lbs.

What do you think?  Will he be ok?

That's a good idea.  However, the doghouse is fully carpeted, floor and walls, and the ceiling is the undercarriage of our motorhome.  It's hard to explain, but he has unusual accommodations!  We really want him to be comfortable, but 18 degrees is still hard to take for any animal.

Well, we did our own thing last night.  Max is not a good house dog at night, so we needed to figure out a way to leave him outside.  I remembered a time when I was very sick and had extreme chills from fever.  My sister filled a 2-liter pop bottle with warm water and put it behind my knees.  Very comforting.  Well, we couldn't get Max to leave his behind his knees but we did fill four of them with hot water and put them in his house and he did just fine overnight.  He was out this morning playing GD when he saw a squirrell trespassing on "his" property.