If your hard up for space can you store some parts outside in 55 gallon drums? I have a couple drums with the steel lid and that u shaped like flange clamp to seal them.

Would likely be fine for unrestored parts. I would hesitate to put anything in them long term that could be harmed by condensation.

Have you seen the Tulsa Belvedere that was buried in a vault? Make 100% sure they are sealed tight and don't put them on the dirt, at least up on blocks...

I would have thought even sealed they'd get condensation in them but maybe not?

The problem becomes: how do you know you have a good seal?
I used to store munitions components in drums, but those had humidity indicators on them that were checked periodically. I can assure you that sealing those drums is "hit and miss." Those drums were also stored inside Butler buildings, out of the weather but not climate controlled. Still the condensation built inside of them (some of them). The method we used to seal them: Snug the closure ring bolt, tap around the edges with a mallet, 2X4, etc. Snug some more, tighten, repeat...until you're confident it's as good as it's gonna get. Check on your parts periodically, and don't get lazy about it.

They do make plastic drums as well. I am not 100% on this but iI would think they would be less prone to "sweating' and they definitely won't rust.
Could also think about filling them with drain oil, vegetable oil (used fryer oil ?), or something similar but cheap,.
Other ideas: a bagged desiccant (some of which can be reused), and or a small fan to pull air through the barrel, think green house fans on amazon.
Also on the drums, see if there are any drum recyclers nearby as you can get them a lot cheaper. There is one locally called Jones Barrel. Not sure on the shipping cost ?

Craigslist always has local people selling a ton of empty plastic barrels from restaurants, farms, etc.