If I wanted to keep rice or rice dust away from a camera, I would tape the camera into a non-glossy paper envelope or brown paper bag. Humidity flows right through paper. Wrapping it in cotton cloth would do the same thing.
But definitely seal the whole thing tightly so the rice pulls water out of the camera, not the entire atmosphere. Maybe inside a Ziploc freezer bag if you don't have a wide-mouth jar with a tight seal. Or two nested freezer bags. That would keep the relative humidity low inside the bag.
You can make uncooked rice into an even stronger desiccant by baking it in a thin layer until just-before-it-turns-light brown. That dries the rice even further and makes it thirstier.
You don't want to let it get brown at all, because that decreases the rice's capacity to absorb water.
I asked the guy who taught me this "what temperature does dry rice turn brown at?", but all he knew was "gas setting # something". You would have to experiment with a small batch, maybe just a few grains on a metal or glass pan.
After you get the rice good and extra-dry, seal it in glass until you dunk a camera or cell phone! Or inside two nested, good-quality Ziploc freezer bags, though the zipper always leaks slowly over enough time.
I haven't tried baking rice myself because I like silica gel as a desiccant. Silica gel is FDA-approved for food applications - it is literally safer than sand. (It's amorphous silica, not crystalline silica.) Silica gel can be regenerated at 250F, or bought at craft stores that have a flower-drying section.
