I have been storing most of my slides in archival sleeves, which are then located in hanging files, for over 20 years. I keep the slides in my house, which is a climate-controlled environment, with temps ranging from maybe 68F during the winter to 78F during the summer, and with humidity levels always around 50% (I have a digital hygrometer to check for humidity). Some of my slides are still in the paper Kodak boxes, and some are still in plastic boxes -- and have been in those boxes for over 15 years. They're just fine -- I checked them recently. I also have a collection of Kodachrome slides taken by my father when he was stationed in Korea during that conflict, which have been stored in a metal box for as long as I can remember, but they also have always been inside houses with their controlled climates, and they are all in excellent condition. If your house has central air/heat -- or if your live in some place like Southern California -- chances are the humidity levels are quite stable, and there is no real need for silica gel and hermetical sealing.