Indeed, a C-130J tanker would have been more suitable for QRA - but an A400M would be even better. If the strangulation of PFI allowed that option....
Given the flying rate in the sun-soaked South Atlantic, it can't do an airliner such as the A330 to be kept sitting out in the open subject to the vagaries of wind and rain. I wouldn't be surprised if corrosion sets in - the weather rots even Land Rovers down there, so I hate to think what it does to high-tech aircraft such as the Voyager.
But the RAF knew about the hangar limitations years ago - so presumably 'own' the risk?