Boxers are NOT outside dogs!!!!!
I feel very sorry for your boxers. They are NOT outside dogs!
I would bet, that their coats are longer, to try and compensate for the cold. Boxers suppose to have short, tight coats, which do NOT do well in temp extremes. Any rescues we have gotten in that have been forced to live outside, their coats are longer and thicker.
I suggest you read the standards and boxer books.
I won't go into breeding here with you, as with your attitude in your post, you won't listen. You think you are an expert, and your not. You are giving out false information to people by stating they are outside dogs and meant to live that way.
Do you have pictures or a web page of your boxers? (nothing is listed in your profile). I would love to see what your boxers look like.