For valuable/collectable knives, Bill's Custom Cases are generally considered best.
Do not use any sort of sealed container (Tupperware, Pelican Cases, etc.) for long-term storage of knives.
Silica Gel is a potential problem; it doesn't make moisture go away, it just holds it much as a sponge holds water. But, if you squeeze a sponge, it will release that water. Under certain conditions, silica gels will release their moisture too. In a sealed container, that can be disasterous.
Avoid foam materials. They trap moisture.
Be careful of cloths and felt. If the dye is not stable, it can, over a long time, stain some knife materials such as bone or ivory.