Sealife Desiccant Moisture Munchers will help prevent condensation from forming inside a housing. Condensation will form in a housing when you take it from warm air to cooler water. Internal camera flashes being fired inside the housing will compound this problem.
Since the silica needs some time to act, give it about 10-15 minutes after closing the housing before entering the water. These 2 gram packs should be used in camera housings and external strobes.