I wasn't satisfied with the storage solution that is included with On The Brink, since it only allows for 3 stacks of unsleeved cards. I sleeve all my cards (to protect and so I can add custom printed cards, etc.).
I was in the same boat. For my solution I took some scissors and cut out the portion of the insert where the cards where supposed to go, I put the cards in tuck boxes (I used one of those tuck box generator websites) and everything fits nice and snug. I still use the petri dishes etc.