XN was outside at Duxford from her arrival until the building of the Superhanger (Hanger 1 which is being converted in theh AirSpace Museum).
The Superhanger was built with restroation of the large airframes in mind.. as the the B-52, Concorde and the Vuclan have all had major restorative work carried out whilst inside.
Conocrde and the Vuclan will be relocated in the AirSpace Museum once its ready...the B-52 is in the AAM.
The airframes do degrade whilst outside but the rate is relatively slow seeing as they are desitned to remain grounded the damage is not necessarily terminal... the XB-70 remianed outside at Wright Patterson for 18 years before going inside...