I can't believe that it is drying that much. I have mid 30% humidity right now and my pvc is keeping 65% humidity so either you are not preparing the reptichip right or there is something else at play drying it. RHPs simply do not dry out substrate like CHEs do.

Unless you have direct airflow across the T8, there is no reason a RHP should dry substrate at the temps you describe. You could always try another substrate like reptile prime and see how it works for you.