As mentioned above I see no need for any heating for any dog kennel.
A stout wooden box sized for the dog,IE twice size,lined with second hand carpet,floor and walls including the ceiling,screwed and battened as some like to tug on any loose bits.
I use a couple of sheets of second hand roofing iron over the top of the box with an 18" cantilevered section over the door way.
A piece of carpet nailed over the inside of the entrance dropping inside that has a split in the middle for the mutt to go through, stops draughts and it closes behind the dog.
A small bale of cereal straw (not hay) is as good as it gets,the dog makes a deep nest and is warm as toast and the straw takes a lot of schitt off their coat too.
One bale will do 1/2 a doz boxes.
Empty the box in summer of the chaff and set again.