thats a big humidor.
I'd start by stuffing a bunch of empty boxes in it......ballast if you will. Chunks of Spanish Cedar, mahogany, etc..........something to help maintain the humidity and reduce the volume of air.
Then I'd "season" it with a bucket of water. I really don't think you need to use distilled water since it is evaporating anyway.
Then I'd maintain the humidity with a **** ton of beads.