Mike; Some forms of cat litter are silica gel. Often called Crystal litter or similar. White crystals with a few blue ones added for looks. Haven't found one that is actually an indicator blue.
Cheapest form of silica gel available. Buy lots, rejuvenate at 120 degrees C often, seal the safe and you are good to go.
No risk of corrosion like the salt solutions and no ongoing cost of buying more DampRid each time the solution saturates.