Cypress mulch is actually very resistant to mold and mildew. It dries out very thoroughly, so misting is important, especially for young ones.
We have kept BRB's for a few years now, and the burrowing in the mulch has never presented problems, but the only time they have practiced burrowing is when they do not have a hide in their enclosure.
Some snakes just like to burrow to feel secure on all sides, but as they grow will very likely take advantage of just the hide.![]()