There are warehouses full of Smithsonian exhibits that can’t be handled in their normal exhibit space. You can contact the museum and arrange tours. The one worth the most time is the air and space storage area. They have some of the last war planes of their type anywhere. Well worth a few hours. When I went about 20 years ago they were working on the Enola Gay.
Enola Gay is now at the Udvar-Hazy (spelling?) annex to the NASM. Much bigger than the NASM, it has a whole lotta flyin’ machines!