I don't have any video DVDs but I have a collection of nearly 700 DVD recordables for storing data, before I offloaded all of them to multiple hard disks. I read up a lot on optimal burning techniques and how to store the discs properly, and hanged out at CDFreaks (a site dedicated to optical media) before it became myce.com. I don't really care much about optical disks nowadays, since haven't burned any discs in ages, but just a comment about silica gel.
Humidity probably plays some role in "DVD rot" so people tend to use some form of dehumidification to lessen the risk. However, I don't know if it's clear to people that using silica gel is useless unless the discs and the gel are sealed together in a container. Ideally this should be airtight, to prevent the gel from saturating quickly, but some kind of non-airtight enclosure will work to some extent, though the ability of the gel will not last long. Moreover, merely placing some silica gel in an enclosure gives you no way of actually knowing if 1) you've decreased the humidity inside sufficiently 2) how long a dehumidified condition inside the enclosure will last.
Therefore, the only really logical way to use silica gel is to use it with an enclosure paired with a hygrometer -- in other words a drybox. A simple example would be a big Lock & Lock or Biokips airtight container with some silica gel and a hygrometer. You can buy digital hygrometers from mall stores or online (Lazada has quite a number), though I'm not sure which ones are accurate. The suggestion in this page to use a junk refrigerator is actually spot on, because the gaskets on a refrigerator make it airtight and it's large enough to hold a large DVD collection. You'll need to put enough silica gel or commercial dehumidifier so that the relative humidity (RH) is below 60%, which is the number to remember because RH of 60% and higher favors mold growth. Targeting something like 30-40% RH would likely be good.
Regarding silica gel, I bought a kilogram of it from a chemical supply store for just 100 pesos many years ago. I no longer use it, but it's stored in several glass bottles to prevent it from being saturated with moisture. If you're gonna use silica gel, it's nice to add a sprinkling of the color change ones, like the ones you can buy at department stores. A kilo of the stuff costs around 800 pesos when I asked many years ago, and there's some concern about the potential carcinogenicity of cobalt chloride, but a small amount should pose no problem, especially since you're not grinding the stuff and creating dust that can be inhaled or ingested. The point of the color change silica gel is that it will tell you when it's saturated with moisture (and therefore no longer effective) and needs to be regenerated (i.e. blue silica gel turns to pink). You can regenerate silica gel by putting it in an oven set to 120 C and heating for an hour or two.
