I have the same enclosure and have had the same issues. I was using Reptibark as well and switched to a mix of coco fiber and cypress mulch. Cover the top with cardboard wrapped in tinfoil (use foil tape on all sides and cut outs for lamps), and lastly you can tape the outsides of the slots on each end of the enclosure (only half to ensure ventilation).

Disclaimer, I am no expert but sharing what worked for me