How can I control humidity levels when curing salami?
Instead of salt, you could get silica gel. These crystals can be found by the bucket, not just in tiny packets. They also make a variety with an indicator that turns pink when they need to be changed.  Bake to refresh them.

Silica gel is amazing stuff.  There is no way you'll not be able to keep the air dry with a mass of absorber tye same scale as the salami.   It's just a matter of how often you'll need to change it.