After you kill the mold / mildew and wipe it down, I've always had luck with setting off one of those chlorine bombs, leave it sealed for 12 hours or so. (and stay away from it)
- Follow on with some Ozone Spray (Ozium, etc) . Finally, when you close it all back up - I recommend putting a desiccant packet (or raw desiccant silica in a sock) in the cabinet to soak up any of this moisture that may still be in the wood (even from cleaning) -
Be sure to give the backbox and main cabinet equal attention.
good luck!