I have managed to make syrup for 6 seasons without a head tank, by just dumping buckets into my preheater pan. I am determined to set one up before this season kicks off. I have been trying to decide between inside the sugarshack or outside for a while.
I do remember MapleFlats saying he mounted his tank flush to the outside wall which allowed the valve to be accessible from the inside through a little cutout in the wall. Eliminates the freezing valve issue but still leaves you with the battle against rain, bugs and ash getting in.