1.
The crisper drawer is actually the MOST humid part of a fridge, not the driest.
2.
All desiccants work by pulling humidity out of the air around it. If the desiccant and the seeds are not sealed together inside something very air-tight, that means that the desiccant will pull air out of the entire atmosphere, until it has exhausted all of its capacity.
To make fresh desiccant actually keep the SEEDS dry, you HAVE TO seal them together in something airtight. I use plastic tubs that once held several pounds of peanuts or peanut butter, but the lids don't seal air-TIGHT. Hence my desiccant packets only last 2-6 months, depending on how often I open the tubs.
Less-tight seals mean you have to replace the desiccant more often, and/or use more of it.
Using those humidity cards is a GREAT idea, it tells you when the desiccant is used up. It would also tell you if you put (say) several tablespoons of fresh dry silica gel into a small jar and then sealed that jar really tight ... it might be able to dry the contents below 10% RH (Relative Humidity), and that would be TOO dry for maximum viable lifetime.
Now I use only one tablespoon or so of silica gel per tub. And i open them often enough that they never get to 10%, or stay there for long.
MAYBE double-bagging inside gallon-size FREEZER bags would keep humidity out. However, regular plastic bags leak pretty fast through the "zipper" and leak slowly right THROUGH the plastic film. Freezer bags are supposed to have a better seal so you get less freezer burn.
