how to prevent mold in condensate pump housing

Does the sump ever go dry?

Anyway, the ideal environment that prevents mold in the pit would be to have the pit covered but not air-tight. It should also be located in the room that's well-ventilated itself. The air movement in the room is probably even more important because there would always be mold in an enclosed room with a sump pit. But if the pit cover has at least some air gaps around the discharge pipe, pump cables etc., it should be enough to prevent mold growth. Of course, it would be even better if you have prolonged periods of time when A/C is not in use and it's not raining much, so the pit has time to dry up and break the mold life cycle.