Corrosion is not a serious issue where we are and the hangar is totally weather tight.
We have a small number of aircraft that have flown here for inclusion in the musuem and we are pretty strict about keeping them in the condition they arrive as far as practical.
Yes, 'while in storage' can be a bit of an issue. Someone grants the museum something which goes on exhibition then 20 years later when the donor dies the family arrive demanding the return of 'their' heirlooms. It is an issue that requires careful handling and the right paper work which I believe in this case is well taken care of.
You should pop across the ditch some time and check out the collection!