Big corrugated culvert and Quonset huts have been buried as temporary military installations. Steel rusts and aluminum and stainless are expensive.
If you want a waterproof container I'd look into used plastic or fiberglass industrial process tanks (preferably ones that held something not too nasty, so likely from the food industry), dig a hole, do proper compaction and gravel base then plop the tanks in (fill them with water or something so they don't float away) and then pour concrete around them for strength (leaving holes for your vents and doors and whatnot). You're going to have to become well versed in chemistry and construction to prevent all your "rooms" from leaking at the doorways where you have cut holes to join them together.
I worked for some time at a former nuclear weapons research facility where a number of Transite composite asbestos Quonset huts were built in the 50's and used through the 2000's.
Checking google maps, it appears that they've finally remediated these structures, but they were in fine condition up until then.
Asbestos ones last a lot longer than the steel ones. The galvanization slowly fails around the edged where there's exposed metal and trapped moisture. They do last a long time but I wouldn't want to put one underground where I couldn't fix it and where any rust hole instantly becomes a leak.
If you want a waterproof container I'd look into used plastic or fiberglass industrial process tanks (preferably ones that held something not too nasty, so likely from the food industry), dig a hole, do proper compaction and gravel base then plop the tanks in (fill them with water or something so they don't float away) and then pour concrete around them for strength (leaving holes for your vents and doors and whatnot). You're going to have to become well versed in chemistry and construction to prevent all your "rooms" from leaking at the doorways where you have cut holes to join them together.