The appropriate methodology for rearing P. indra minori in totes or closed containers is to only provide a few sprigs of fresh host both morning and evening.  By regulating the amount of host, excess humidity within the environment is avoided allowing frass to dry.  It is also critical to remove frass morning and evening.  Keep only 1 fifth instar in each container.  Taking these precautions for indra swallowtails can seem burdensome, but it will produce healthy caterpillars.  (Assuming, of course, you are properly managing host plant cuttings.)