Welcome to ATP, MtGypsy!
I agree that keeping stored seeds extra-dry adds a lot to the time they stay viable.
Kew Royal Botanic Gardens, and other sources, say that the length of time that many seeds stay viable approximately doubles for every 10% reduction in their relative humidity (HOW dry they were dried and and kept).
Kew: theory of desiccants and RH
http://www.kew.org/ucm/groups/...
When the old silica gel packets lose their potency, you can buy more silica gel from any craft store with a flower-drying isle. I get a pound and a half for around $7.
I put about a tablespoonful in a coin envelope (folded stapled paper would do) and keep that in a tightly sealed plastic tub. Desiccants stay effective longer if kept in tightly-sealed containers. Otherwise they soak up their entire capacity from the atmosphere and can't absorb any more humidity.
Or automotive shops sell inexpensive "Oil-Sorb" or "Oil-Dry ( Bentonite clay containing Montmorillonite).
Or you can bake some dry rice at a low temperature NOT letting it get brown.
They say that dried milk powder is also a desiccant.
http://garden.org/ideas/view/R...
I'm working on an "Idea" about desiccants, but I need some photos before it's ready. here are some of the links I collected for it:
Kew Millennium Seed Bank Project, long-term seed storage containers:
http://www.kew.org/ucm/groups/...
Many Kew Royal Botanic Gardens "Technical Information Sheets" about collecting and storing seeds, written by Millennium Seed Bank staff:
http://www.kew.org/science-res...
P.S. If you like gadgets, you can buy humidity-indicating cards:
Drierite relative humidity cards at 40 cents each:
https://secure.drierite.com/ca...
ULINE humidity cards, $18 / 100 cards
http://www.uline.com/BL_1002/H...
http://www.uline.com/Product/D...
