Kent, you can use "florist foam" moistened with "PG solution" (50%/50% propylene glycol and distilled water) -- the solution is sold online, such as Cigars International (3 8 oz. containers for $10). Simply place the foam in a suitable plastic container, and drill holes in the cover. You can monitor proper humidity with a hygrometer, recharging the foam with more solution when needed.
Boveda packs (65% RH are best) work very well and are reliable, but are expensive, particularly if the plan is to rely on the packs to humidify a large container because you'll need a bunch of them.
Heartfelt Beads are also an effective and reliable method.
I also suggest you peruse the CG article on using Kitty Litter" for humidification -- a very inexpensive, reliable method.
