Eagles Over the Kennebec

The best solution I ever found for frozen doors and locks is a dry lubricant called 'Tri-Flow', which is really big in the bicycle world as a chain lubricant. It's teflon-based and doesn't either gum up (WD-40) or clump up (graphite or moly based lubricants), plus it is non-conductive. Squirt it in and on all the hinges, locks and keyholes of the doors and you won't have another frozen door all winter. (I admit, not tested in Maine or Manitoba, but very much tested in a really bad Michigan winter many years ago.)