Use silica gel packet in housing if there is room for it to absorb moisture from air in housing. Or put camera and housing in a plastic ziplock bag with gel packet and leave for a while and then close housing before opening the bag. ( old timer showed me this with expensive camera / electronics equipment in tropics as old housings were very tight tolerances and days of preventing mould on real film or inside of lenses) My only warning is some electronics and things rely / need / designed fo some level of moisture in the parts / seals to work so don't store and let things get sucked totally dry.
http://www.silicagel.com.au/
I've used this with other gear as well and original rain x on outside of visors . Most of these coatings change the optics slightly and correct application on clean lens and correct cloth are critical.
http://www.rainx.com/product/glass-a...ainx-anti-fog/
Like with everything always do a test if you don't know someone using the exact product with your housing long term. I've stuffed / discoloured some older expensive housings trying different things and spotless clean with pure detergent , compressed air and a silica pouch is my fallback. Still hurts wrecking even cheap gear. Avoid any amonia based glass cleaners or solvent based ones.