I like Boveda for small jobs but for my cooler-dor I use Heartfelt Beads. Try seasoning with the wet sponge method then switch to the beads. My cooler-dor is
almost maintenance free. BTW, the relative in relative humidity means relative to temprature. If the cooling mechanism is cycling on and off, doing its job, then you'll see the fluctuation you're seeing. I'm guessing that your Boveda packs are still absorbing moisture from your sponge, preventing your RH from climbing higher. With them so dry, they
will absorb moisture below 84%. If you use only the sponge method, you should see better seasoning results; then switch to beads.
Good luck!