I bought my first rack....sterilite tubs with flexwatt.....I personally use a herpstat. We are now building another rack and I have sterilites to put in it with flexwatt....again with another herpstat. We have not built the rack so they are just in tubs with the flexwatt. No problems.....just make sure you don't just leave the tub on the floor ......I put wood slats underneath to get an airflow.