https://iosafe.com/productsOne thing, if you're only worried about moisture, you can do some basic ziplock bags. Pelican and similar cases are about physical protection in addition to the water seals. The fire protection is only for documents and such - a hard drive will die at a much lower temperature than the 400 degrees paper can handle.
What other backups are you maintaining, and how often will you update what is in the safe deposit box? If you rely on the safe copy for theft / corruption / drive failure, you're fine not protecting it from water. In the event of a flood event, what is the elevation at your residence compared to the safe deposit box? How much do you travel and does it prevent some sort of bug out style of bag where you'd have a copy on you?
If it's worth that much, how about a safe deposit box above the flood line - anything that survived Katrina would be fine.
Also decide if online is a better value, ala BackBlaze or such, or a relative who's outside the flood zone that you regularly send a drive to.