MPA isn't exactly Heathrow, building a single large tin shed will not entail demolishing the whole place and starting again...
Have you any
idea of the cost of building an A330-capable hangar even in the UK, let alone at MPA? Unlike at Heathrow, any hangar at MPA has very high winds with which to cope, so must be a massive structure. It's not like throwing up a new branch of B&Q!
Unlike scheduled departures, the QRA tanker has to be kept at high RS. That can be achieved if the aircraft is tugged out from the hangar, but to keep it ready 24/7 out in the open would cost a fortune in de-icing. No doubt the environmentalists would also be concerned at all that de-icing fluid entering the local ecosystem...
C-130, VC10K, TriStar, KDC-10, B707 and KC-767 will all fit the Timmy hangar, as will A400M. Voyager will not.