I keep Damp Rid in enclosed storage areas and change them out every couple of months. Have also been known to run heat from a space heater and A/C to reduce humidity when in a cool humid area. Our biggest areas are the windshield, the outermost storage area under the bed exposed to the cold outside, storage under the dinnette booths and husband's closet ( he doesn't get into it 15 times a day like I do mine LOL ). You can purchase these type of things at Dollar Tree for $1 each. Sometimes in near cleaning supplies, other times near fabric storage and closet storage items.
