I keep all my gear in two HPRC cases. Go Pelican or HPRC brand. Both water tight and can take SERIOUS KNOCK AROUNDS!!!
When you do this, you need to keep desiccant packs in the cases are it does no good. If the air is humid when you latch the case, you're just trapping that humid air in the case. Desiccant packs will absorb that moisture. You can find packs that re-usable. After they become saturated, they turn pink (I think some may turn blue). You then just toss them n a low temp oven for a specified period of time to dry them out for re-use.
I usually pack my cases upstairs before I take them down to the basement. I will be sure to get Desiccant packs as I have heard they help for long term storage. I usually open the cases once a week. should I still pack Desiccant even though I pack upstairs?
I would still keep some desiccant in the case. You will spend $10 for the desiccant to give you moisture protection on thousands of dollars in gear. It's a no brainier.
5d Mark III, 7d Mark II, 24mm f/1.4L II, 24-105 f/4L IS, 70-200 f/2.8L IS II, 100 f/2.8L IS macro, 135 f/2L, 3x 600EX-RT, ST-E3-RT, EF 1.4x III